diff --git a/.cursor/rules/lab-notifications.mdc b/.cursor/rules/lab-notifications.mdc
new file mode 100644
index 0000000..065781d
--- /dev/null
+++ b/.cursor/rules/lab-notifications.mdc
@@ -0,0 +1,14 @@
+---
+description: Lab tab badges — activity model, tab-counts API, read cursors
+globs: backend/src/modules/notifications/**,backend/src/common/lab-case-activity.ts,frontend/src/lib/hooks/useTabBadgeCounts.ts,frontend/src/lib/tabBadgeUtils.ts,frontend/src/lib/api/notifications.ts,frontend/src/components/ui/shared/NavBadgePill.tsx,frontend/src/components/ui/shared/Sidebar.tsx
+alwaysApply: false
+---
+
+# Lab tab badges
+
+- **Split counts (Option B):** Lab Cases = sent + clinic comments + important; Lab Tasks = completions + lab comments; Clinic Treatment = visible lab comments + completions.
+- **API:** `GET /notifications/tab-counts`; Tasks/Treatment mark read on tab visit; Cases uses per-case read + `hasUnread` on list cards.
+- **Pattern:** `useTabBadgeCounts` + `notifyTabBadgesChanged()` — same shape as `usePendingConnectionsCount`.
+- **Orgs connections badge** stays on separate `pending-count` endpoint.
+
+Full map: `.cursor/skills/lab-notifications/SKILL.md`
diff --git a/.cursor/skills/lab-notifications/SKILL.md b/.cursor/skills/lab-notifications/SKILL.md
new file mode 100644
index 0000000..6bd84b0
--- /dev/null
+++ b/.cursor/skills/lab-notifications/SKILL.md
@@ -0,0 +1,56 @@
+---
+name: dyolink-lab-notifications
+description: Lab case activity feed + sidebar tab badge counts. Use when changing notifications API, LabCaseActivity, read state, or Sidebar badges for Cases/Tasks/Treatment.
+---
+
+# Lab notifications (tab badges)
+
+Backend: [`backend/src/modules/notifications/`](backend/src/modules/notifications/)  
+Activity types: [`backend/src/common/lab-case-activity.ts`](backend/src/common/lab-case-activity.ts)  
+Frontend hook: [`frontend/src/lib/hooks/useTabBadgeCounts.ts`](frontend/src/lib/hooks/useTabBadgeCounts.ts)
+
+## Models
+
+- **`LabCaseActivity`** — append-only events: `CASE_SENT`, `CLINIC_COMMENT`, `LAB_COMMENT`, `CASE_IMPORTANT`, `CASE_AMENDED` (stub for Step 7), `TASK_COMPLETED`
+- **`LabCaseUserTabReadState`** — per user/org/tab cursor (`TASKS` | `TREATMENT`) for sidebar badge clearing on tab visit. **Cases tab** uses per-case read instead (see below).
+- **`LabCaseUserReadState`** — per user/org/labCase cursor; drives Cases tab count and `hasUnread` on case list cards
+
+## Tab badge buckets (Option B — split lab counts)
+
+| Org | Tab | Activity types |
+|-----|-----|----------------|
+| LAB | Cases | `CASE_SENT`, `CLINIC_COMMENT`, `CASE_IMPORTANT` |
+| LAB | Tasks | `TASK_COMPLETED`, `LAB_COMMENT` |
+| CLINIC | Treatment | `LAB_COMMENT` (only `visibleToClinic`), `TASK_COMPLETED` |
+
+Counts exclude events where `actorUserId === current user`. Clinic `LAB_COMMENT` counts only when `payload.visibleToClinic === true`.
+
+## APIs
+
+- `GET /notifications/tab-counts` → `{ cases?, tasks?, treatment? }` — **Cases** count = number of cases with unread Cases-bucket activity (per-case read cursor)
+- `POST /notifications/mark-tab-read` `{ tab }` — Tasks + Treatment only (Cases skips tab-level clear)
+- `POST /notifications/mark-case-read` `{ labCaseId }` — opening a case clears that case’s unread dot and updates Cases tab count
+
+## Emit activity from
+
+| Event | Service |
+|-------|---------|
+| First send | `treatments.service` `sendLabCase` → `CASE_SENT` |
+| Comment | `lab-case-comments.service` → `CLINIC_COMMENT` / `LAB_COMMENT` |
+| Mark important | `cases.service` `updateImportant` (only when set true) → `CASE_IMPORTANT` |
+| Task completed | `tasks.service` `updateStatus` → `TASK_COMPLETED` |
+
+After mutations, frontend calls `notifyTabBadgesChanged()` (window event).
+
+## Frontend pattern (same as org connections)
+
+- `useTabBadgeCounts()` — fetch on pathname change + `tab-badges-changed` event
+- `useMarkTabReadOnVisit()` — Tasks + Treatment pages only (Cases badge clears when opening unread cases)
+- `NavBadgePill` in [`Sidebar.tsx`](frontend/src/components/ui/shared/Sidebar.tsx)
+- **Organizations** pending connections still use `usePendingConnectionsCount` (separate pending-state API)
+
+## Out of scope (later steps)
+
+- Push / email / websockets
+- Activity feed UI (Step 6)
+- `CASE_AMENDED` emit (Step 7)
diff --git a/.cursor/skills/lab-tasks/SKILL.md b/.cursor/skills/lab-tasks/SKILL.md
index ac984cc..d9db181 100644
--- a/.cursor/skills/lab-tasks/SKILL.md
+++ b/.cursor/skills/lab-tasks/SKILL.md
@@ -86,6 +86,10 @@ Keep changes minimal — match existing `sm:` breakpoint patterns elsewhere in t
 - **Tasks filters:** filter `<select>`s use the same 44px mobile height as other form controls.
 - **Treatment lab dispatch:** shipment card `p-3 sm:p-4`; **Send to lab** is `w-full sm:w-auto`.
 
+## Tab badges
+
+See `.cursor/skills/lab-notifications/SKILL.md` — split lab Cases/Tasks counts, clinic Treatment; `useTabBadgeCounts` + `notifyTabBadgesChanged`.
+
 ## Permissions
 
 `TAB_TASKS_READ` / `TAB_TASKS_EDIT`; `LabOrgGuard` on all task routes.
diff --git a/AGENTS.md b/AGENTS.md
index 30e5907..9913a8c 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -45,7 +45,7 @@ frontend/src/
 - **History filters** are client-side only (`treatmentHistoryFilters.ts`): “Not shipped to lab” + single date on already-fetched patient history; includes live current draft when filtering.
 - **Lab case comments** on a detail when sent and lab case tasks are not all `COMPLETED` (`taskProgress` from API).
 
-**Lab Tasks tab:** Newest case first; steps ordered 1→N; case grouping when sorted by date; `stepCompleted` filter; prosthesis colors from `PROSTHESIS_TYPE_COLORS` via catalog; task assignment in **Cases** (compact row: status + assignee + last update); on **Tasks**, all staff see every task but only assignee (or unassigned pool) can change status — others see “Assigned to {name}” instead of the status dropdown; **case due dates** set/edited in clinic Treatment lab dispatch, shown on lab Cases/Tasks with overdue filter + sort; **mobile:** larger task status controls, sticky case header when grouped — see `.cursor/skills/lab-tasks/SKILL.md`.
+**Lab Tasks tab:** Newest case first; steps ordered 1→N; case grouping when sorted by date; `stepCompleted` filter; prosthesis colors from `PROSTHESIS_TYPE_COLORS` via catalog; task assignment in **Cases** (compact row: status + assignee + last update); on **Tasks**, all staff see every task but only assignee (or unassigned pool) can change status — others see “Assigned to {name}” instead of the status dropdown; **case due dates** set/edited in clinic Treatment lab dispatch, shown on lab Cases/Tasks with overdue filter + sort; **mobile:** larger task status controls, sticky case header when grouped; **tab badges:** `LabCaseActivity` + `GET /notifications/tab-counts` (lab Cases/Tasks split, clinic Treatment) — see `.cursor/skills/lab-tasks/SKILL.md` and `.cursor/skills/lab-notifications/SKILL.md`.
 
 ## Backend layout
 
@@ -70,6 +70,7 @@ Errors: `AppException` + `ErrorCode` → frontend `getUserFacingError()`. Never
 | `.cursor/skills/add-feature/` | New tab, API module, or end-to-end feature |
 | `.cursor/skills/treatment-workspace/` | Treatment tab: preview vs form, history, load flow, drafts |
 | `.cursor/skills/lab-tasks/` | Lab Tasks tab: sort, case grouping, step-completed filter, prosthesis colors |
+| `.cursor/skills/lab-notifications/` | Tab badges: LabCaseActivity, tab-counts API, read cursors |
 | `.cursor/skills/frontend-structure/` | Moving components, auditing folder layout |
 | `.cursor/skills/api-errors/` | New backend errors + frontend translations |
 
diff --git a/backend/prisma/migrations/20260713160000_lab_case_activity/migration.sql b/backend/prisma/migrations/20260713160000_lab_case_activity/migration.sql
new file mode 100644
index 0000000..adb423e
--- /dev/null
+++ b/backend/prisma/migrations/20260713160000_lab_case_activity/migration.sql
@@ -0,0 +1,59 @@
+-- Lab case activity feed + per-user read cursors for tab badges
+
+CREATE TYPE "LabCaseActivityType" AS ENUM (
+  'CASE_SENT',
+  'CLINIC_COMMENT',
+  'LAB_COMMENT',
+  'CASE_IMPORTANT',
+  'CASE_AMENDED',
+  'TASK_COMPLETED'
+);
+
+CREATE TYPE "LabCaseTabReadTarget" AS ENUM ('CASES', 'TASKS', 'TREATMENT');
+
+CREATE TABLE "lab_case_activities" (
+  "id" TEXT NOT NULL,
+  "labCaseId" TEXT NOT NULL,
+  "type" "LabCaseActivityType" NOT NULL,
+  "actorUserId" TEXT,
+  "payload" JSONB,
+  "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  CONSTRAINT "lab_case_activities_pkey" PRIMARY KEY ("id")
+);
+
+CREATE TABLE "lab_case_user_read_states" (
+  "userId" TEXT NOT NULL,
+  "organizationId" TEXT NOT NULL,
+  "labCaseId" TEXT NOT NULL,
+  "lastReadAt" TIMESTAMP(3) NOT NULL,
+  CONSTRAINT "lab_case_user_read_states_pkey" PRIMARY KEY ("userId", "organizationId", "labCaseId")
+);
+
+CREATE TABLE "lab_case_user_tab_read_states" (
+  "userId" TEXT NOT NULL,
+  "organizationId" TEXT NOT NULL,
+  "tab" "LabCaseTabReadTarget" NOT NULL,
+  "lastReadAt" TIMESTAMP(3) NOT NULL,
+  CONSTRAINT "lab_case_user_tab_read_states_pkey" PRIMARY KEY ("userId", "organizationId", "tab")
+);
+
+ALTER TABLE "lab_case_activities"
+  ADD CONSTRAINT "lab_case_activities_labCaseId_fkey"
+  FOREIGN KEY ("labCaseId") REFERENCES "lab_cases"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+ALTER TABLE "lab_case_activities"
+  ADD CONSTRAINT "lab_case_activities_actorUserId_fkey"
+  FOREIGN KEY ("actorUserId") REFERENCES "users"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+ALTER TABLE "lab_case_user_read_states"
+  ADD CONSTRAINT "lab_case_user_read_states_labCaseId_fkey"
+  FOREIGN KEY ("labCaseId") REFERENCES "lab_cases"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+CREATE INDEX "lab_case_activities_labCaseId_createdAt_idx"
+  ON "lab_case_activities"("labCaseId", "createdAt");
+
+CREATE INDEX "lab_case_activities_type_createdAt_idx"
+  ON "lab_case_activities"("type", "createdAt");
+
+CREATE INDEX "lab_case_user_read_states_userId_organizationId_idx"
+  ON "lab_case_user_read_states"("userId", "organizationId");
diff --git a/backend/prisma/schema.prisma b/backend/prisma/schema.prisma
index 6191431..02be3d9 100644
--- a/backend/prisma/schema.prisma
+++ b/backend/prisma/schema.prisma
@@ -28,6 +28,7 @@ model User {
   assignedLabCaseTasks LabCaseTask[] @relation("LabCaseTaskAssignee")
   labCaseTaskStatusEvents LabCaseTaskStatusEvent[]
   labCaseComments LabCaseComment[]
+  labCaseActivities LabCaseActivity[]
   phoneVerificationCodes PhoneVerificationCode[]
 
   createdAt DateTime @default(now())
@@ -224,6 +225,8 @@ model LabCase {
   toothProsthesis LabCaseToothProsthesis[]
   comments        LabCaseComment[]
   attachments     LabCaseAttachment[]
+  activities      LabCaseActivity[]
+  userReadStates  LabCaseUserReadState[]
 
   @@index([treatmentId, sortOrder])
   @@map("lab_cases")
@@ -410,6 +413,60 @@ model LabCaseComment {
   @@map("lab_case_comments")
 }
 
+enum LabCaseActivityType {
+  CASE_SENT
+  CLINIC_COMMENT
+  LAB_COMMENT
+  CASE_IMPORTANT
+  CASE_AMENDED
+  TASK_COMPLETED
+}
+
+enum LabCaseTabReadTarget {
+  CASES
+  TASKS
+  TREATMENT
+}
+
+model LabCaseActivity {
+  id          String              @id @default(uuid())
+  labCaseId   String
+  type        LabCaseActivityType
+  actorUserId String?
+  payload     Json?
+  createdAt   DateTime            @default(now())
+
+  labCase   LabCase @relation(fields: [labCaseId], references: [id], onDelete: Cascade)
+  actorUser User?   @relation(fields: [actorUserId], references: [id], onDelete: SetNull)
+
+  @@index([labCaseId, createdAt])
+  @@index([type, createdAt])
+  @@map("lab_case_activities")
+}
+
+model LabCaseUserReadState {
+  userId         String
+  organizationId String
+  labCaseId      String
+  lastReadAt     DateTime
+
+  labCase LabCase @relation(fields: [labCaseId], references: [id], onDelete: Cascade)
+
+  @@id([userId, organizationId, labCaseId])
+  @@index([userId, organizationId])
+  @@map("lab_case_user_read_states")
+}
+
+model LabCaseUserTabReadState {
+  userId         String
+  organizationId String
+  tab            LabCaseTabReadTarget
+  lastReadAt     DateTime
+
+  @@id([userId, organizationId, tab])
+  @@map("lab_case_user_tab_read_states")
+}
+
 model Plan {
   id       String @id @default(uuid())
   name     String @unique // "Solo", "Small", "Medium", "Large", "Enterprise"
diff --git a/backend/src/app.module.ts b/backend/src/app.module.ts
index 0eb8045..2df331d 100644
--- a/backend/src/app.module.ts
+++ b/backend/src/app.module.ts
@@ -18,6 +18,7 @@ import { CatalogModule } from './modules/catalog/catalog.module';
 import { ProsthesisCatalogModule } from './modules/prosthesis-catalog/prosthesis-catalog.module';
 import { LabCaseCommentsModule } from './modules/lab-case-comments/lab-case-comments.module';
 import { TodayModule } from './modules/today/today.module';
+import { NotificationsModule } from './modules/notifications/notifications.module';
 
 @Module({
   imports: [
@@ -39,6 +40,7 @@ import { TodayModule } from './modules/today/today.module';
     StaffModule,
     OrganizationModule,
     TodayModule,
+    NotificationsModule,
     AdminModule.forRoot(),
   ],
   controllers: [AppController],
diff --git a/backend/src/common/lab-case-activity.ts b/backend/src/common/lab-case-activity.ts
new file mode 100644
index 0000000..c20723c
--- /dev/null
+++ b/backend/src/common/lab-case-activity.ts
@@ -0,0 +1,20 @@
+import { LabCaseActivityType } from '@prisma/client';
+
+/** Lab Cases tab — new shipments, clinic comments, important flag. */
+export const LAB_CASES_TAB_ACTIVITY_TYPES: LabCaseActivityType[] = [
+  LabCaseActivityType.CASE_SENT,
+  LabCaseActivityType.CLINIC_COMMENT,
+  LabCaseActivityType.CASE_IMPORTANT,
+];
+
+/** Lab Tasks tab — task completions and lab-side comments. */
+export const LAB_TASKS_TAB_ACTIVITY_TYPES: LabCaseActivityType[] = [
+  LabCaseActivityType.TASK_COMPLETED,
+  LabCaseActivityType.LAB_COMMENT,
+];
+
+/** Clinic Treatment tab — visible lab comments and task progress. */
+export const CLINIC_TREATMENT_TAB_ACTIVITY_TYPES: LabCaseActivityType[] = [
+  LabCaseActivityType.LAB_COMMENT,
+  LabCaseActivityType.TASK_COMPLETED,
+];
diff --git a/backend/src/modules/cases/cases.module.ts b/backend/src/modules/cases/cases.module.ts
index 6bd4a71..baafc43 100644
--- a/backend/src/modules/cases/cases.module.ts
+++ b/backend/src/modules/cases/cases.module.ts
@@ -1,12 +1,13 @@
 import { Module } from '@nestjs/common';
 import { PrismaService } from '../../../prisma/prisma.service';
 import { LabOrgGuard } from '../../common/guards/lab-org.guard';
+import { NotificationsModule } from '../notifications/notifications.module';
 import { TreatmentCatalogModule } from '../treatment-catalog/treatment-catalog.module';
 import { CasesController } from './cases.controller';
 import { CasesService } from './cases.service';
 
 @Module({
-  imports: [TreatmentCatalogModule],
+  imports: [TreatmentCatalogModule, NotificationsModule],
   controllers: [CasesController],
   providers: [CasesService, PrismaService, LabOrgGuard],
   exports: [CasesService],
diff --git a/backend/src/modules/cases/cases.service.ts b/backend/src/modules/cases/cases.service.ts
index 4a1325a..195fa4a 100644
--- a/backend/src/modules/cases/cases.service.ts
+++ b/backend/src/modules/cases/cases.service.ts
@@ -5,7 +5,7 @@ import {
   NotFoundException,
 } from '@nestjs/common';
 import { createReadStream, existsSync } from 'fs';
-import { CatalogEntityKind, LabTaskStatus, Prisma } from '@prisma/client';
+import { CatalogEntityKind, LabCaseActivityType, LabTaskStatus, Prisma } from '@prisma/client';
 import { PrismaService } from '../../../prisma/prisma.service';
 import { normalizeMobile } from '../../common/phone';
 import {
@@ -20,6 +20,8 @@ import {
 } from '../../common/lab-case-due-date';
 import { normalizeTaskTeeth } from './lab-case-task.util';
 import { hasEffectivePermission } from '../../common/membership-permissions';
+import { LAB_CASES_TAB_ACTIVITY_TYPES } from '../../common/lab-case-activity';
+import { LabCaseActivityService } from '../notifications/lab-case-activity.service';
 
 const labCaseListInclude = {
   treatment: {
@@ -92,6 +94,7 @@ export class CasesService {
     private readonly prisma: PrismaService,
     private readonly treatmentCatalog: TreatmentCatalogService,
     private readonly catalogLabels: CatalogLabelService,
+    private readonly labCaseActivity: LabCaseActivityService,
   ) {}
 
   getOrganizationIdFromUser(user: { organizationId?: string }) {
@@ -138,10 +141,21 @@ export class CasesService {
       this.prisma.labCase.count({ where }),
     ]);
 
+    const unreadCaseIds = await this.labCaseActivity.unreadCaseIdsInBatch(
+      actorUserId,
+      labOrganizationId,
+      items.map((lc) => lc.id),
+      LAB_CASES_TAB_ACTIVITY_TYPES,
+      'LAB',
+    );
+
     return {
       success: true,
       data: {
-        items: items.map((lc) => this.mapLabCaseListItem(lc)),
+        items: items.map((lc) => ({
+          ...this.mapLabCaseListItem(lc),
+          hasUnread: unreadCaseIds.has(lc.id),
+        })),
         pagination: {
           page,
           limit,
@@ -356,7 +370,7 @@ export class CasesService {
         sentAt: { not: null },
         sends: { some: { organizationId: labOrganizationId } },
       },
-      select: { id: true },
+      select: { id: true, isImportant: true },
     });
 
     if (!existing) {
@@ -368,6 +382,14 @@ export class CasesService {
       data: { isImportant: dto.isImportant },
     });
 
+    if (dto.isImportant && !existing.isImportant) {
+      await this.labCaseActivity.record({
+        labCaseId,
+        type: LabCaseActivityType.CASE_IMPORTANT,
+        actorUserId,
+      });
+    }
+
     const labCase = await this.prisma.labCase.findFirstOrThrow({
       where: { id: labCaseId },
       include: labCaseListInclude,
diff --git a/backend/src/modules/lab-case-comments/lab-case-comments.module.ts b/backend/src/modules/lab-case-comments/lab-case-comments.module.ts
index e6f8abd..a3fe4f5 100644
--- a/backend/src/modules/lab-case-comments/lab-case-comments.module.ts
+++ b/backend/src/modules/lab-case-comments/lab-case-comments.module.ts
@@ -1,10 +1,12 @@
 import { Module } from '@nestjs/common';
 import { PrismaService } from '../../../prisma/prisma.service';
 import { LabOrgGuard } from '../../common/guards/lab-org.guard';
+import { NotificationsModule } from '../notifications/notifications.module';
 import { LabCaseCommentsController } from './lab-case-comments.controller';
 import { LabCaseCommentsService } from './lab-case-comments.service';
 
 @Module({
+  imports: [NotificationsModule],
   controllers: [LabCaseCommentsController],
   providers: [LabCaseCommentsService, PrismaService, LabOrgGuard],
   exports: [LabCaseCommentsService],
diff --git a/backend/src/modules/lab-case-comments/lab-case-comments.service.ts b/backend/src/modules/lab-case-comments/lab-case-comments.service.ts
index 4d74b13..79f3d46 100644
--- a/backend/src/modules/lab-case-comments/lab-case-comments.service.ts
+++ b/backend/src/modules/lab-case-comments/lab-case-comments.service.ts
@@ -3,10 +3,11 @@ import {
   Injectable,
   NotFoundException,
 } from '@nestjs/common';
-import { LabCaseCommentSide, Prisma } from '@prisma/client';
+import { LabCaseCommentSide, LabCaseActivityType, Prisma } from '@prisma/client';
 import { PrismaService } from '../../../prisma/prisma.service';
 import { CreateLabCaseCommentDto } from './dto/lab-case-comment.dto';
 import { hasEffectivePermission } from '../../common/membership-permissions';
+import { LabCaseActivityService } from '../notifications/lab-case-activity.service';
 
 const commentInclude = {
   authorUser: { select: { id: true, name: true } },
@@ -19,7 +20,10 @@ type CommentWithRelations = Prisma.LabCaseCommentGetPayload<{
 
 @Injectable()
 export class LabCaseCommentsService {
-  constructor(private readonly prisma: PrismaService) {}
+  constructor(
+    private readonly prisma: PrismaService,
+    private readonly labCaseActivity: LabCaseActivityService,
+  ) {}
 
   // ---------- Lab side (TAB_TASKS_EDIT) ----------
 
@@ -47,6 +51,15 @@ export class LabCaseCommentsService {
       },
       include: commentInclude,
     });
+    await this.labCaseActivity.record({
+      labCaseId: caseId,
+      type: LabCaseActivityType.LAB_COMMENT,
+      actorUserId,
+      payload: {
+        commentId: created.id,
+        visibleToClinic: created.visibleToClinic,
+      },
+    });
     return { success: true, data: this.mapComment(created, LabCaseCommentSide.LAB) };
   }
 
@@ -104,6 +117,12 @@ export class LabCaseCommentsService {
       },
       include: commentInclude,
     });
+    await this.labCaseActivity.record({
+      labCaseId: caseId,
+      type: LabCaseActivityType.CLINIC_COMMENT,
+      actorUserId,
+      payload: { commentId: created.id },
+    });
     return { success: true, data: this.mapComment(created, LabCaseCommentSide.CLINIC) };
   }
 
@@ -140,6 +159,12 @@ export class LabCaseCommentsService {
       },
       include: commentInclude,
     });
+    await this.labCaseActivity.record({
+      labCaseId: caseId,
+      type: LabCaseActivityType.CLINIC_COMMENT,
+      actorUserId,
+      payload: { commentId: created.id },
+    });
     return { success: true, data: this.mapComment(created, LabCaseCommentSide.CLINIC) };
   }
 
diff --git a/backend/src/modules/notifications/dto/notifications.dto.ts b/backend/src/modules/notifications/dto/notifications.dto.ts
new file mode 100644
index 0000000..90f8667
--- /dev/null
+++ b/backend/src/modules/notifications/dto/notifications.dto.ts
@@ -0,0 +1,12 @@
+import { IsEnum, IsUUID } from 'class-validator';
+import { LabCaseTabReadTarget } from '@prisma/client';
+
+export class MarkTabReadDto {
+  @IsEnum(LabCaseTabReadTarget)
+  tab!: LabCaseTabReadTarget;
+}
+
+export class MarkCaseReadDto {
+  @IsUUID()
+  labCaseId!: string;
+}
diff --git a/backend/src/modules/notifications/lab-case-activity.service.ts b/backend/src/modules/notifications/lab-case-activity.service.ts
new file mode 100644
index 0000000..de69a95
--- /dev/null
+++ b/backend/src/modules/notifications/lab-case-activity.service.ts
@@ -0,0 +1,331 @@
+import {
+  ForbiddenException,
+  Injectable,
+  NotFoundException,
+} from '@nestjs/common';
+import {
+  LabCaseActivityType,
+  LabCaseTabReadTarget,
+  Prisma,
+} from '@prisma/client';
+import { PrismaService } from '../../../prisma/prisma.service';
+import { hasEffectivePermission } from '../../common/membership-permissions';
+import {
+  CLINIC_TREATMENT_TAB_ACTIVITY_TYPES,
+  LAB_CASES_TAB_ACTIVITY_TYPES,
+  LAB_TASKS_TAB_ACTIVITY_TYPES,
+} from '../../common/lab-case-activity';
+
+type TxClient = Prisma.TransactionClient;
+
+@Injectable()
+export class LabCaseActivityService {
+  constructor(private readonly prisma: PrismaService) {}
+
+  async record(
+    input: {
+      labCaseId: string;
+      type: LabCaseActivityType;
+      actorUserId?: string | null;
+      payload?: Prisma.InputJsonValue;
+    },
+    tx?: TxClient,
+  ) {
+    const client = tx ?? this.prisma;
+    await client.labCaseActivity.create({
+      data: {
+        labCaseId: input.labCaseId,
+        type: input.type,
+        actorUserId: input.actorUserId ?? null,
+        payload: input.payload ?? undefined,
+      },
+    });
+  }
+
+  async getTabCounts(userId: string, organizationId: string) {
+    const org = await this.prisma.organization.findUnique({
+      where: { id: organizationId },
+      include: { type: true },
+    });
+    if (!org) {
+      throw new NotFoundException('Organization not found');
+    }
+
+    await this.assertMembership(userId, organizationId);
+
+    const orgType = org.type.name;
+    const tabReads = await this.prisma.labCaseUserTabReadState.findMany({
+      where: { userId, organizationId },
+    });
+    const tabSince = (tab: LabCaseTabReadTarget) =>
+      tabReads.find((row) => row.tab === tab)?.lastReadAt ?? new Date(0);
+
+    if (orgType === 'LAB') {
+      const [cases, tasks] = await Promise.all([
+        this.countUnreadLabCasesForCasesTab(userId, organizationId),
+        this.countUnreadForTab(
+          userId,
+          organizationId,
+          'LAB',
+          LAB_TASKS_TAB_ACTIVITY_TYPES,
+          tabSince(LabCaseTabReadTarget.TASKS),
+        ),
+      ]);
+      return { success: true, data: { cases, tasks } };
+    }
+
+    if (orgType === 'CLINIC') {
+      const treatment = await this.countUnreadForTab(
+        userId,
+        organizationId,
+        'CLINIC',
+        CLINIC_TREATMENT_TAB_ACTIVITY_TYPES,
+        tabSince(LabCaseTabReadTarget.TREATMENT),
+      );
+      return { success: true, data: { treatment } };
+    }
+
+    return { success: true, data: {} };
+  }
+
+  async markTabRead(userId: string, organizationId: string, tab: LabCaseTabReadTarget) {
+    await this.assertMembership(userId, organizationId);
+    const now = new Date();
+    await this.prisma.labCaseUserTabReadState.upsert({
+      where: {
+        userId_organizationId_tab: { userId, organizationId, tab },
+      },
+      create: { userId, organizationId, tab, lastReadAt: now },
+      update: { lastReadAt: now },
+    });
+    return { success: true };
+  }
+
+  /** Cases with unread activity in the Cases tab bucket (per-case read cursor, not tab visit). */
+  async countUnreadLabCasesForCasesTab(
+    userId: string,
+    organizationId: string,
+  ): Promise<number> {
+    const grouped = await this.prisma.labCaseActivity.groupBy({
+      by: ['labCaseId'],
+      where: {
+        type: { in: LAB_CASES_TAB_ACTIVITY_TYPES },
+        labCase: {
+          sentAt: { not: null },
+          sends: { some: { organizationId } },
+        },
+        OR: [{ actorUserId: null }, { actorUserId: { not: userId } }],
+      },
+      _max: { createdAt: true },
+    });
+
+    if (grouped.length === 0) return 0;
+
+    const caseIds = grouped.map((row) => row.labCaseId);
+    const readStates = await this.prisma.labCaseUserReadState.findMany({
+      where: { userId, organizationId, labCaseId: { in: caseIds } },
+    });
+    const readMap = new Map(readStates.map((row) => [row.labCaseId, row.lastReadAt]));
+
+    return grouped.filter((row) => {
+      const since = readMap.get(row.labCaseId) ?? new Date(0);
+      return (row._max.createdAt ?? new Date(0)) > since;
+    }).length;
+  }
+
+  async unreadCaseIdsInBatch(
+    userId: string,
+    organizationId: string,
+    labCaseIds: string[],
+    types: LabCaseActivityType[],
+    orgType: 'LAB' | 'CLINIC',
+  ): Promise<Set<string>> {
+    if (labCaseIds.length === 0) return new Set();
+
+    const readStates = await this.prisma.labCaseUserReadState.findMany({
+      where: { userId, organizationId, labCaseId: { in: labCaseIds } },
+    });
+    const sinceByCase = new Map(
+      labCaseIds.map((id) => [
+        id,
+        readStates.find((row) => row.labCaseId === id)?.lastReadAt ?? new Date(0),
+      ]),
+    );
+
+    const clinicLabCommentFilter = this.clinicLabCommentFilter(orgType);
+    const activities = await this.prisma.labCaseActivity.findMany({
+      where: {
+        labCaseId: { in: labCaseIds },
+        type: { in: types },
+        AND: [
+          { OR: [{ actorUserId: null }, { actorUserId: { not: userId } }] },
+          ...(Object.keys(clinicLabCommentFilter).length ? [clinicLabCommentFilter] : []),
+        ],
+      },
+      select: { labCaseId: true, createdAt: true },
+    });
+
+    const unread = new Set<string>();
+    for (const activity of activities) {
+      const since = sinceByCase.get(activity.labCaseId)!;
+      if (activity.createdAt > since) {
+        unread.add(activity.labCaseId);
+      }
+    }
+    return unread;
+  }
+
+  async markCaseRead(userId: string, organizationId: string, labCaseId: string) {
+    await this.assertMembership(userId, organizationId);
+    await this.assertCanAccessCase(userId, organizationId, labCaseId);
+
+    const now = new Date();
+    await this.prisma.labCaseUserReadState.upsert({
+      where: {
+        userId_organizationId_labCaseId: { userId, organizationId, labCaseId },
+      },
+      create: { userId, organizationId, labCaseId, lastReadAt: now },
+      update: { lastReadAt: now },
+    });
+    return { success: true };
+  }
+
+  private async countUnreadForTab(
+    userId: string,
+    organizationId: string,
+    orgType: 'LAB' | 'CLINIC',
+    types: LabCaseActivityType[],
+    since: Date,
+  ): Promise<number> {
+    const labCaseScope =
+      orgType === 'LAB'
+        ? {
+            sentAt: { not: null },
+            sends: { some: { organizationId } },
+          }
+        : {
+            sentAt: { not: null },
+            treatment: { organizationId },
+          };
+
+    const clinicLabCommentFilter = this.clinicLabCommentFilter(orgType);
+
+    return this.prisma.labCaseActivity.count({
+      where: {
+        type: { in: types },
+        createdAt: { gt: since },
+        labCase: labCaseScope,
+        AND: [
+          {
+            OR: [{ actorUserId: null }, { actorUserId: { not: userId } }],
+          },
+          clinicLabCommentFilter,
+        ],
+      },
+    });
+  }
+
+  private clinicLabCommentFilter(orgType: 'LAB' | 'CLINIC'): Prisma.LabCaseActivityWhereInput {
+    if (orgType !== 'CLINIC') return {};
+    return {
+      OR: [
+        { type: { not: LabCaseActivityType.LAB_COMMENT } },
+        {
+          type: LabCaseActivityType.LAB_COMMENT,
+          payload: { path: ['visibleToClinic'], equals: true },
+        },
+      ],
+    };
+  }
+
+  private async assertMembership(userId: string, organizationId: string) {
+    const membership = await this.prisma.membership.findFirst({
+      where: {
+        userId,
+        organizationId,
+        OR: [{ isOwner: true }, { isActive: true }],
+      },
+    });
+    if (!membership) {
+      throw new ForbiddenException('You are not a member of this organization');
+    }
+  }
+
+  private async assertCanAccessCase(
+    userId: string,
+    organizationId: string,
+    labCaseId: string,
+  ) {
+    const org = await this.prisma.organization.findUnique({
+      where: { id: organizationId },
+      include: { type: true },
+    });
+    if (!org) {
+      throw new NotFoundException('Organization not found');
+    }
+
+    const labCase = await this.prisma.labCase.findFirst({
+      where:
+        org.type.name === 'LAB'
+          ? {
+              id: labCaseId,
+              sentAt: { not: null },
+              sends: { some: { organizationId } },
+            }
+          : {
+              id: labCaseId,
+              treatment: { organizationId },
+            },
+      select: { id: true },
+    });
+
+    if (!labCase) {
+      throw new NotFoundException('Case not found');
+    }
+
+    if (org.type.name === 'LAB') {
+      const membership = await this.prisma.membership.findFirst({
+        where: {
+          userId,
+          organizationId,
+          OR: [{ isOwner: true }, { isActive: true }],
+        },
+        include: {
+          permissions: { include: { permission: true } },
+          organization: { include: { type: true, plan: true } },
+        },
+      });
+      if (
+        !membership ||
+        !(
+          hasEffectivePermission(membership, 'TAB_CASES_READ') ||
+          hasEffectivePermission(membership, 'TAB_TASKS_READ')
+        )
+      ) {
+        throw new ForbiddenException('You do not have access to this case');
+      }
+      return;
+    }
+
+    const membership = await this.prisma.membership.findFirst({
+      where: {
+        userId,
+        organizationId,
+        OR: [{ isOwner: true }, { isActive: true }],
+      },
+      include: {
+        permissions: { include: { permission: true } },
+        organization: { include: { type: true, plan: true } },
+      },
+    });
+    if (
+      !membership ||
+      !(
+        hasEffectivePermission(membership, 'TAB_TREATMENT_READ') ||
+        hasEffectivePermission(membership, 'TAB_TREATMENT_EDIT')
+      )
+    ) {
+      throw new ForbiddenException('You do not have access to this case');
+    }
+  }
+}
diff --git a/backend/src/modules/notifications/notifications.controller.ts b/backend/src/modules/notifications/notifications.controller.ts
new file mode 100644
index 0000000..2198b6e
--- /dev/null
+++ b/backend/src/modules/notifications/notifications.controller.ts
@@ -0,0 +1,53 @@
+import { Body, Controller, Get, Post, Req, UseGuards } from '@nestjs/common';
+import { ApiBearerAuth, ApiOperation, ApiTags } from '@nestjs/swagger';
+import { JwtAuthGuard } from '../auth/guards/jwt-auth.guard';
+import { MarkCaseReadDto, MarkTabReadDto } from './dto/notifications.dto';
+import { LabCaseActivityService } from './lab-case-activity.service';
+
+@ApiTags('notifications')
+@ApiBearerAuth('JWT-auth')
+@UseGuards(JwtAuthGuard)
+@Controller('notifications')
+export class NotificationsController {
+  constructor(private readonly labCaseActivityService: LabCaseActivityService) {}
+
+  @Get('tab-counts')
+  @ApiOperation({ summary: 'Unread activity counts for sidebar tab badges' })
+  getTabCounts(@Req() req: { user: { id: string; organizationId?: string } }) {
+    const organizationId = req.user.organizationId;
+    if (!organizationId) {
+      return { success: true, data: {} };
+    }
+    return this.labCaseActivityService.getTabCounts(req.user.id, organizationId);
+  }
+
+  @Post('mark-tab-read')
+  @ApiOperation({ summary: 'Clear sidebar badge for a tab after the user visits it' })
+  markTabRead(
+    @Body() dto: MarkTabReadDto,
+    @Req() req: { user: { id: string; organizationId?: string } },
+  ) {
+    const organizationId = req.user.organizationId;
+    if (!organizationId) {
+      return { success: true };
+    }
+    return this.labCaseActivityService.markTabRead(req.user.id, organizationId, dto.tab);
+  }
+
+  @Post('mark-case-read')
+  @ApiOperation({ summary: 'Mark a lab case as read for the current user' })
+  markCaseRead(
+    @Body() dto: MarkCaseReadDto,
+    @Req() req: { user: { id: string; organizationId?: string } },
+  ) {
+    const organizationId = req.user.organizationId;
+    if (!organizationId) {
+      return { success: true };
+    }
+    return this.labCaseActivityService.markCaseRead(
+      req.user.id,
+      organizationId,
+      dto.labCaseId,
+    );
+  }
+}
diff --git a/backend/src/modules/notifications/notifications.module.ts b/backend/src/modules/notifications/notifications.module.ts
new file mode 100644
index 0000000..805af2e
--- /dev/null
+++ b/backend/src/modules/notifications/notifications.module.ts
@@ -0,0 +1,10 @@
+import { Module } from '@nestjs/common';
+import { LabCaseActivityService } from './lab-case-activity.service';
+import { NotificationsController } from './notifications.controller';
+
+@Module({
+  controllers: [NotificationsController],
+  providers: [LabCaseActivityService],
+  exports: [LabCaseActivityService],
+})
+export class NotificationsModule {}
diff --git a/backend/src/modules/tasks/tasks.module.ts b/backend/src/modules/tasks/tasks.module.ts
index d65d0b7..b26340a 100644
--- a/backend/src/modules/tasks/tasks.module.ts
+++ b/backend/src/modules/tasks/tasks.module.ts
@@ -1,10 +1,11 @@
 import { Module } from '@nestjs/common';
 import { CatalogModule } from '../catalog/catalog.module';
+import { NotificationsModule } from '../notifications/notifications.module';
 import { TasksController } from './tasks.controller';
 import { TasksService } from './tasks.service';
 
 @Module({
-  imports: [CatalogModule],
+  imports: [CatalogModule, NotificationsModule],
   controllers: [TasksController],
   providers: [TasksService],
 })
diff --git a/backend/src/modules/tasks/tasks.service.ts b/backend/src/modules/tasks/tasks.service.ts
index 454ea08..41e3c42 100644
--- a/backend/src/modules/tasks/tasks.service.ts
+++ b/backend/src/modules/tasks/tasks.service.ts
@@ -4,7 +4,7 @@ import {
   Injectable,
   NotFoundException,
 } from '@nestjs/common';
-import { CatalogEntityKind, LabTaskStatus, Prisma } from '@prisma/client';
+import { CatalogEntityKind, LabCaseActivityType, LabTaskStatus, Prisma } from '@prisma/client';
 import { PrismaService } from '../../../prisma/prisma.service';
 import { normalizeMobile } from '../../common/phone';
 import {
@@ -15,6 +15,7 @@ import { normalizeTaskTeeth } from '../cases/lab-case-task.util';
 import { isLabCaseOverdue, startOfUtcDay } from '../../common/lab-case-due-date';
 import { ListLabTasksDto, LocateTaskPageDto, UpdateLabTaskDto } from './dto/tasks.dto';
 import { hasEffectivePermission } from '../../common/membership-permissions';
+import { LabCaseActivityService } from '../notifications/lab-case-activity.service';
 
 const taskListInclude = {
   lastStatusChangedBy: { select: { id: true, name: true } },
@@ -37,6 +38,7 @@ export class TasksService {
   constructor(
     private readonly prisma: PrismaService,
     private readonly catalogLabels: CatalogLabelService,
+    private readonly labCaseActivity: LabCaseActivityService,
   ) {}
 
   getOrganizationIdFromUser(user: { organizationId?: string }) {
@@ -205,6 +207,18 @@ export class TasksService {
         });
       }
 
+      if (dto.status === LabTaskStatus.COMPLETED && task.status !== LabTaskStatus.COMPLETED) {
+        await this.labCaseActivity.record(
+          {
+            labCaseId: task.labCaseId,
+            type: LabCaseActivityType.TASK_COMPLETED,
+            actorUserId,
+            payload: { taskId },
+          },
+          tx,
+        );
+      }
+
       return result;
     });
 
diff --git a/backend/src/modules/treatments/treatments.module.ts b/backend/src/modules/treatments/treatments.module.ts
index a819eea..24f345c 100644
--- a/backend/src/modules/treatments/treatments.module.ts
+++ b/backend/src/modules/treatments/treatments.module.ts
@@ -3,11 +3,12 @@ import { PrismaService } from '../../../prisma/prisma.service';
 import { ClinicOrgGuard } from '../../common/guards/clinic-org.guard';
 import { ProsthesisCatalogModule } from '../prosthesis-catalog/prosthesis-catalog.module';
 import { LabCaseCommentsModule } from '../lab-case-comments/lab-case-comments.module';
+import { NotificationsModule } from '../notifications/notifications.module';
 import { TreatmentsController } from './treatments.controller';
 import { TreatmentsService } from './treatments.service';
 
 @Module({
-  imports: [ProsthesisCatalogModule, LabCaseCommentsModule],
+  imports: [ProsthesisCatalogModule, LabCaseCommentsModule, NotificationsModule],
   controllers: [TreatmentsController],
   providers: [TreatmentsService, PrismaService, ClinicOrgGuard],
 })
diff --git a/backend/src/modules/treatments/treatments.service.ts b/backend/src/modules/treatments/treatments.service.ts
index 14372c0..1556529 100644
--- a/backend/src/modules/treatments/treatments.service.ts
+++ b/backend/src/modules/treatments/treatments.service.ts
@@ -4,7 +4,7 @@ import {
   Injectable,
   NotFoundException,
 } from '@nestjs/common';
-import { LabTaskStatus, LinkStatus, Prisma } from '@prisma/client';
+import { LabCaseActivityType, LabTaskStatus, LinkStatus, Prisma } from '@prisma/client';
 import { createReadStream, existsSync, mkdirSync } from 'fs';
 import { join } from 'path';
 import { randomUUID } from 'crypto';
@@ -21,6 +21,7 @@ import {
   isLabCaseFullyCompleted,
   parseDueDateInput,
 } from '../../common/lab-case-due-date';
+import { LabCaseActivityService } from '../notifications/lab-case-activity.service';
 import {
   generateTreatmentTitle,
   normalizeTeeth,
@@ -83,6 +84,7 @@ export class TreatmentsService {
     private readonly prisma: PrismaService,
     private readonly treatmentCatalog: TreatmentCatalogService,
     private readonly prosthesisCatalog: ProsthesisCatalogService,
+    private readonly labCaseActivity: LabCaseActivityService,
   ) {}
 
   getOrganizationIdFromUser(user: { organizationId?: string }) {
@@ -558,6 +560,7 @@ export class TreatmentsService {
     }
 
     const now = new Date();
+    const isFirstSend = !labCase.sentAt;
 
     await this.prisma.$transaction(async (tx) => {
       await tx.labCaseSend.create({
@@ -575,6 +578,17 @@ export class TreatmentsService {
       }
 
       await generateLabCaseTasks(tx, labCaseId, actorLanguage);
+
+      if (isFirstSend) {
+        await this.labCaseActivity.record(
+          {
+            labCaseId,
+            type: LabCaseActivityType.CASE_SENT,
+            actorUserId,
+          },
+          tx,
+        );
+      }
     });
 
     const refreshed = await this.prisma.labCase.findUniqueOrThrow({
diff --git a/frontend/messages/en.json b/frontend/messages/en.json
index d7fa3b9..f8dae15 100644
--- a/frontend/messages/en.json
+++ b/frontend/messages/en.json
@@ -428,6 +428,7 @@
     "statusInProgress": "In progress",
     "statusCompleted": "Completed",
     "importantLabel": "Important",
+    "unreadCase": "Unread updates",
     "markCaseImportant": "Mark case as important",
     "markImportant": "Mark as important",
     "lastUpdatedBy": "Updated by {name}",
diff --git a/frontend/messages/fa.json b/frontend/messages/fa.json
index 82448f4..019b9a9 100644
--- a/frontend/messages/fa.json
+++ b/frontend/messages/fa.json
@@ -428,6 +428,7 @@
     "statusInProgress": "در حال انجام",
     "statusCompleted": "انجام شده",
     "importantLabel": "مهم",
+    "unreadCase": "به‌روزرسانی‌های خوانده‌نشده",
     "markCaseImportant": "علامت‌گذاری پرونده به‌عنوان مهم",
     "markImportant": "علامت‌گذاری به عنوان مهم",
     "lastUpdatedBy": "به‌روزرسانی توسط {name}",
diff --git a/frontend/messages/nl.json b/frontend/messages/nl.json
index 315298f..44bfbd7 100644
--- a/frontend/messages/nl.json
+++ b/frontend/messages/nl.json
@@ -428,6 +428,7 @@
     "statusInProgress": "Bezig",
     "statusCompleted": "Voltooid",
     "importantLabel": "Belangrijk",
+    "unreadCase": "Ongelezen updates",
     "markCaseImportant": "Zaak als belangrijk markeren",
     "markImportant": "Markeren als belangrijk",
     "lastUpdatedBy": "Bijgewerkt door {name}",
diff --git a/frontend/src/components/ui/lab/CasesPage.tsx b/frontend/src/components/ui/lab/CasesPage.tsx
index f3601e8..a1208a4 100644
--- a/frontend/src/components/ui/lab/CasesPage.tsx
+++ b/frontend/src/components/ui/lab/CasesPage.tsx
@@ -14,6 +14,8 @@ import {
   formatPatientName,
 } from '@/components/lab/caseDetailUtils';
 import { LabCaseDueDateBadge } from '@/components/lab/LabCaseDueDateBadge';
+import { notificationsApi } from '@/lib/api/notifications';
+import { notifyTabBadgesChanged } from '@/lib/tabBadgeUtils';
 import { casesApi } from '@/lib/api/cases';
 import { tasksApi } from '@/lib/api/tasks';
 import { treatmentCatalogApi } from '@/lib/api/treatment-catalog';
@@ -184,6 +186,14 @@ export function CasesPage() {
   useEffect(() => {
     if (selectedCaseId) {
       void loadDetail(selectedCaseId);
+      void notificationsApi.markCaseRead(selectedCaseId).then(() => {
+        notifyTabBadgesChanged();
+        setCases((prev) =>
+          prev.map((item) =>
+            item.id === selectedCaseId ? { ...item, hasUnread: false } : item,
+          ),
+        );
+      });
       void tasksApi
         .listComments(selectedCaseId)
         .then((r) => setCommentCount(r.data.length))
@@ -244,6 +254,7 @@ export function CasesPage() {
           item.id === selectedCaseId ? { ...item, isImportant: response.data.isImportant } : item,
         ),
       );
+      notifyTabBadgesChanged();
     } catch (error: unknown) {
       setSelectedCase(previousCase);
       toast.showError(getUserFacingError(error, tErrors, t('errorUpdateTask')));
@@ -373,19 +384,27 @@ export function CasesPage() {
                             : 'border-border hover:border-primary/40'
                         }`}
                       >
-                        <div className="flex flex-wrap items-center gap-1.5">
-                          <div className="font-medium text-text-primary">
-                            {formatPatientName(item.patient)}
+                        <div className="flex items-center gap-2">
+                          <div className="flex min-w-0 flex-1 flex-wrap items-center gap-1.5">
+                            <div className="font-medium text-text-primary">
+                              {formatPatientName(item.patient)}
+                            </div>
+                            <LabCaseDueDateBadge
+                              dueDate={item.dueDate}
+                              locale={locale}
+                              className="text-[10px]"
+                            />
+                            {item.isImportant ? (
+                              <Badge variant="warning" fixedWidth={false}>
+                                {t('importantLabel')}
+                              </Badge>
+                            ) : null}
                           </div>
-                          <LabCaseDueDateBadge
-                            dueDate={item.dueDate}
-                            locale={locale}
-                            className="text-[10px]"
-                          />
-                          {item.isImportant ? (
-                            <Badge variant="warning" fixedWidth={false}>
-                              {t('importantLabel')}
-                            </Badge>
+                          {item.hasUnread ? (
+                            <span
+                              className="h-2 w-2 shrink-0 rounded-full bg-badge-warning-fg"
+                              aria-label={t('unreadCase')}
+                            />
                           ) : null}
                         </div>
                         <div className="text-xs text-text-muted mt-0.5">
@@ -495,6 +514,7 @@ export function CasesPage() {
                           visibleToClinic,
                         });
                         setCommentCount((n) => n + 1);
+                        notifyTabBadgesChanged();
                         return r.data;
                       }}
                       onToggleVisibility={async (commentId, visible) => {
diff --git a/frontend/src/components/ui/lab/TaskRow.tsx b/frontend/src/components/ui/lab/TaskRow.tsx
index 445f6db..a6d09a7 100644
--- a/frontend/src/components/ui/lab/TaskRow.tsx
+++ b/frontend/src/components/ui/lab/TaskRow.tsx
@@ -12,6 +12,7 @@ import {
   labTaskStatusVariant,
 } from '@/components/lab/labTaskStatusDisplay';
 import { LabCaseDueDateBadge } from '@/components/lab/LabCaseDueDateBadge';
+import { notifyTabBadgesChanged } from '@/lib/tabBadgeUtils';
 import {
   formatToothList,
   prosthesisTypeBadgeStyleFromCatalog,
@@ -228,6 +229,7 @@ export function TaskRow({
                 body,
                 visibleToClinic,
               });
+              notifyTabBadgesChanged();
               return r.data;
             }}
             onToggleVisibility={async (commentId, visible) => {
diff --git a/frontend/src/components/ui/lab/TasksPage.tsx b/frontend/src/components/ui/lab/TasksPage.tsx
index d7a2044..5cc44e1 100644
--- a/frontend/src/components/ui/lab/TasksPage.tsx
+++ b/frontend/src/components/ui/lab/TasksPage.tsx
@@ -16,6 +16,8 @@ import {
   isDefaultTasksView,
   TASK_COMPLETE_EXIT_MS,
 } from '@/components/lab/tasksViewDefaults';
+import { useMarkTabReadOnVisit } from '@/lib/hooks/useTabBadgeCounts';
+import { notifyTabBadgesChanged } from '@/lib/tabBadgeUtils';
 import { scrollWithinMainScrollContainer } from '@/components/shared/scrollWithinMain';
 import { getUserFacingError } from '@/components/shared/formatApiError';
 import { canEditTasks, canViewTasks } from '@/components/shared/permissions';
@@ -78,6 +80,7 @@ export function TasksPage() {
   const canView = canViewTasks(currentOrganization);
   const canEdit = canEditTasks(currentOrganization);
   const locale = user?.language ?? 'en';
+  useMarkTabReadOnVisit();
 
   const tRef = useRef(t);
   tRef.current = t;
@@ -273,6 +276,7 @@ export function TasksPage() {
         } else {
           await loadTasks();
         }
+        notifyTabBadgesChanged();
       } catch (error: unknown) {
         showError(getUserFacingError(error, tErrors, t('errorUpdateTask')));
       } finally {
diff --git a/frontend/src/components/ui/shared/NavBadgePill.tsx b/frontend/src/components/ui/shared/NavBadgePill.tsx
new file mode 100644
index 0000000..f578f69
--- /dev/null
+++ b/frontend/src/components/ui/shared/NavBadgePill.tsx
@@ -0,0 +1,17 @@
+interface NavBadgePillProps {
+  count: number;
+  ariaLabel: string;
+}
+
+export function NavBadgePill({ count, ariaLabel }: NavBadgePillProps) {
+  if (count <= 0) return null;
+
+  return (
+    <span
+      className="min-w-[1.25rem] rounded-full bg-badge-warning-bg px-1.5 py-0.5 text-center text-xs font-medium tabular-nums text-badge-warning-fg border border-badge-warning-border"
+      aria-label={ariaLabel}
+    >
+      {count > 99 ? '99+' : count}
+    </span>
+  );
+}
diff --git a/frontend/src/components/ui/shared/Sidebar.tsx b/frontend/src/components/ui/shared/Sidebar.tsx
index dc006fa..4fc1000 100644
--- a/frontend/src/components/ui/shared/Sidebar.tsx
+++ b/frontend/src/components/ui/shared/Sidebar.tsx
@@ -18,6 +18,9 @@ import {
 import type { OrgTypeName } from '@/components/shared/permissions';
 import { useAuth } from '@/lib/hooks/useAuth';
 import { usePendingConnectionsCount } from '@/lib/hooks/usePendingConnectionsCount';
+import { useTabBadgeCounts } from '@/lib/hooks/useTabBadgeCounts';
+import { badgeCountForPath } from '@/lib/tabBadgeUtils';
+import { NavBadgePill } from '@/components/ui/shared/NavBadgePill';
 import {
   canViewAppointmentsTab,
   canViewCases,
@@ -48,6 +51,7 @@ function Sidebar({ mobileOpen = false, onClose }: SidebarProps) {
   const pathname = usePathname();
   const { currentOrganization } = useAuth();
   const pendingConnectionsCount = usePendingConnectionsCount();
+  const tabBadgeCounts = useTabBadgeCounts();
   const orgType = currentOrganization?.type;
 
   const menu = useMemo((): MenuItem[] => {
@@ -119,6 +123,7 @@ function Sidebar({ mobileOpen = false, onClose }: SidebarProps) {
           const isActive = pathname === item.path;
           const showPendingBadge =
             item.path === '/organizations' && pendingConnectionsCount > 0;
+          const tabBadgeCount = badgeCountForPath(tabBadgeCounts, item.path);
 
           return (
             <Link
@@ -134,14 +139,13 @@ function Sidebar({ mobileOpen = false, onClose }: SidebarProps) {
             >
               <Icon className="w-[18px] h-[18px] icon-flat" />
               <span className="text-sm flex-1">{item.name}</span>
-              {showPendingBadge && (
-                <span
-                  className="min-w-[1.25rem] rounded-full bg-badge-warning-bg px-1.5 py-0.5 text-center text-xs font-medium tabular-nums text-badge-warning-fg border border-badge-warning-border"
-                  aria-label={`${pendingConnectionsCount} pending connection requests`}
-                >
-                  {pendingConnectionsCount}
-                </span>
-              )}
+              {showPendingBadge ? (
+                <NavBadgePill
+                  count={pendingConnectionsCount}
+                  ariaLabel={`${pendingConnectionsCount} pending connection requests`}
+                />
+              ) : null}
+              <NavBadgePill count={tabBadgeCount} ariaLabel={`${tabBadgeCount} unread updates`} />
             </Link>
           );
         })}
diff --git a/frontend/src/components/ui/treatment/TreatmentWorkspace.tsx b/frontend/src/components/ui/treatment/TreatmentWorkspace.tsx
index 224e536..f83c454 100644
--- a/frontend/src/components/ui/treatment/TreatmentWorkspace.tsx
+++ b/frontend/src/components/ui/treatment/TreatmentWorkspace.tsx
@@ -35,6 +35,9 @@ import type { LabDispatchAttentionItem } from '@/components/treatment/labDispatc
 import { collectLabDispatchAttention } from '@/components/treatment/labDispatchAttention';
 import { canEditTreatment, canViewTreatment, canAccessDashboardRoute } from '@/components/shared/permissions';
 import { scrollWithinMainScrollContainer } from '@/components/shared/scrollWithinMain';
+import { useMarkTabReadOnVisit } from '@/lib/hooks/useTabBadgeCounts';
+import { notificationsApi } from '@/lib/api/notifications';
+import { notifyTabBadgesChanged } from '@/lib/tabBadgeUtils';
 import { getUserFacingError } from '@/components/shared/formatApiError';
 import { useToast } from '@/lib/hooks/useToast';
 import type { Organization } from '@/types/organization';
@@ -275,6 +278,7 @@ export function TreatmentWorkspace({
   const { showError, showSuccess, messages: toastMessages } = useToast();
   const canView = canViewTreatment(currentOrganization);
   const canEdit = canEditTreatment(currentOrganization);
+  useMarkTabReadOnVisit();
 
   const [stripHidden, setStripHidden] = useState(false);
   const todayStart = useMemo(() => startOfLocalDay(new Date()), []);
@@ -346,6 +350,18 @@ export function TreatmentWorkspace({
     [labCaseDrafts],
   );
 
+  const activeSentLabCaseId = useMemo(() => {
+    const match = labCaseDrafts.find(
+      (lc) => lc.detailClientId === activeDetailId && lc.sentAt && lc.id,
+    );
+    return match?.id ?? null;
+  }, [labCaseDrafts, activeDetailId]);
+
+  useEffect(() => {
+    if (!activeSentLabCaseId) return;
+    void notificationsApi.markCaseRead(activeSentLabCaseId).then(() => notifyTabBadgesChanged());
+  }, [activeSentLabCaseId]);
+
   const isDirty = useMemo(
     () => isDetailsDirty(details, savedSnapshot),
     [details, savedSnapshot],
@@ -1205,6 +1221,7 @@ export function TreatmentWorkspace({
           return [orgId, ...prev.filter((id) => id !== orgId)].slice(0, 10);
         });
         showSuccess(t('successCaseSent'));
+        notifyTabBadgesChanged();
       } catch (error: unknown) {
         showError(getUserFacingError(error, tErrors, t('errorSendCase')));
       } finally {
diff --git a/frontend/src/lib/api/notifications.ts b/frontend/src/lib/api/notifications.ts
new file mode 100644
index 0000000..37e43cf
--- /dev/null
+++ b/frontend/src/lib/api/notifications.ts
@@ -0,0 +1,19 @@
+import { apiClient } from '@/lib/api/client';
+import type { LabCaseTabReadTarget, TabBadgeCounts } from '@/lib/tabBadgeUtils';
+
+export const notificationsApi = {
+  tabCounts: async (): Promise<{ success: boolean; data: TabBadgeCounts }> => {
+    const response = await apiClient.get('/notifications/tab-counts');
+    return response.data;
+  },
+
+  markTabRead: async (tab: LabCaseTabReadTarget): Promise<{ success: boolean }> => {
+    const response = await apiClient.post('/notifications/mark-tab-read', { tab });
+    return response.data;
+  },
+
+  markCaseRead: async (labCaseId: string): Promise<{ success: boolean }> => {
+    const response = await apiClient.post('/notifications/mark-case-read', { labCaseId });
+    return response.data;
+  },
+};
diff --git a/frontend/src/lib/hooks/useTabBadgeCounts.ts b/frontend/src/lib/hooks/useTabBadgeCounts.ts
new file mode 100644
index 0000000..03da398
--- /dev/null
+++ b/frontend/src/lib/hooks/useTabBadgeCounts.ts
@@ -0,0 +1,60 @@
+'use client';
+
+import { useCallback, useEffect, useState } from 'react';
+import { usePathname } from '@/i18n/navigation';
+import { notificationsApi } from '@/lib/api/notifications';
+import {
+  tabBadgesChangedEventName,
+  tabFromPathname,
+  type TabBadgeCounts,
+} from '@/lib/tabBadgeUtils';
+import { useAuth } from '@/lib/hooks/useAuth';
+
+const EMPTY_COUNTS: TabBadgeCounts = {};
+
+export function useTabBadgeCounts(): TabBadgeCounts {
+  const pathname = usePathname();
+  const { currentOrganization } = useAuth();
+  const [counts, setCounts] = useState<TabBadgeCounts>(EMPTY_COUNTS);
+
+  const fetchCounts = useCallback(async () => {
+    if (!currentOrganization?.id) {
+      setCounts(EMPTY_COUNTS);
+      return;
+    }
+
+    try {
+      const res = await notificationsApi.tabCounts();
+      setCounts(res.data ?? EMPTY_COUNTS);
+    } catch {
+      setCounts(EMPTY_COUNTS);
+    }
+  }, [currentOrganization?.id]);
+
+  useEffect(() => {
+    void fetchCounts();
+  }, [fetchCounts, pathname]);
+
+  useEffect(() => {
+    const onChanged = () => void fetchCounts();
+    window.addEventListener(tabBadgesChangedEventName(), onChanged);
+    return () => window.removeEventListener(tabBadgesChangedEventName(), onChanged);
+  }, [fetchCounts]);
+
+  return counts;
+}
+
+export function useMarkTabReadOnVisit() {
+  const pathname = usePathname();
+  const { currentOrganization } = useAuth();
+
+  useEffect(() => {
+    const tab = tabFromPathname(pathname);
+    // Cases tab badge clears per opened case (mark-case-read), not on tab visit.
+    if (!tab || tab === 'CASES' || !currentOrganization?.id) return;
+
+    void notificationsApi.markTabRead(tab).then(() => {
+      window.dispatchEvent(new Event(tabBadgesChangedEventName()));
+    });
+  }, [pathname, currentOrganization?.id]);
+}
diff --git a/frontend/src/lib/tabBadgeUtils.ts b/frontend/src/lib/tabBadgeUtils.ts
new file mode 100644
index 0000000..236c4c6
--- /dev/null
+++ b/frontend/src/lib/tabBadgeUtils.ts
@@ -0,0 +1,31 @@
+export type TabBadgeCounts = {
+  cases?: number;
+  tasks?: number;
+  treatment?: number;
+};
+
+export type LabCaseTabReadTarget = 'CASES' | 'TASKS' | 'TREATMENT';
+
+const TAB_BADGES_CHANGED_EVENT = 'tab-badges-changed';
+
+export function notifyTabBadgesChanged() {
+  window.dispatchEvent(new Event(TAB_BADGES_CHANGED_EVENT));
+}
+
+export function tabBadgesChangedEventName() {
+  return TAB_BADGES_CHANGED_EVENT;
+}
+
+export function tabFromPathname(pathname: string): LabCaseTabReadTarget | null {
+  if (pathname === '/cases' || pathname.startsWith('/cases/')) return 'CASES';
+  if (pathname === '/tasks' || pathname.startsWith('/tasks/')) return 'TASKS';
+  if (pathname === '/treatment' || pathname.startsWith('/treatment/')) return 'TREATMENT';
+  return null;
+}
+
+export function badgeCountForPath(counts: TabBadgeCounts, pathname: string): number {
+  if (pathname === '/cases' || pathname.startsWith('/cases/')) return counts.cases ?? 0;
+  if (pathname === '/tasks' || pathname.startsWith('/tasks/')) return counts.tasks ?? 0;
+  if (pathname === '/treatment' || pathname.startsWith('/treatment/')) return counts.treatment ?? 0;
+  return 0;
+}
diff --git a/frontend/src/types/cases.ts b/frontend/src/types/cases.ts
index a41956a..6ddd122 100644
--- a/frontend/src/types/cases.ts
+++ b/frontend/src/types/cases.ts
@@ -6,6 +6,7 @@ export interface LabCaseListItem {
   dueDate: string | null;
   isOverdue: boolean;
   isImportant: boolean;
+  hasUnread: boolean;
   clinic: { id: string; name: string };
   patient: {
     id: string;