diff --git a/server/src/services/adminService.ts b/server/src/services/adminService.ts
index 66a2d349..f17dd8ba 100644
--- a/server/src/services/adminService.ts
+++ b/server/src/services/adminService.ts
@@ -8,6 +8,7 @@ import { updateJwtSecret } from '../config';
 import { maybe_encrypt_api_key, decrypt_api_key } from './apiKeyCrypto';
 import { getAllPermissions, savePermissions as savePerms, PERMISSION_ACTIONS } from './permissions';
 import { revokeUserSessions, revokeUserSessionsForClient } from '../mcp';
+import { deleteUserCompletely } from './userCleanupService';
 import { validatePassword } from './passwordPolicy';
 import { getPhotoProviderConfig } from './memories/helpersService';
 import { send as sendNotification } from './notificationService';
@@ -170,7 +171,7 @@ export function deleteUser(id: string, currentUserId: number) {
   const userToDel = db.prepare('SELECT id, email FROM users WHERE id = ?').get(id) as { id: number; email: string } | undefined;
   if (!userToDel) return { error: 'User not found', status: 404 };
 
-  db.prepare('DELETE FROM users WHERE id = ?').run(id);
+  deleteUserCompletely(userToDel.id);
   return { email: userToDel.email };
 }
 
diff --git a/server/src/services/authService.ts b/server/src/services/authService.ts
index 3917e64b..0bbcbfc7 100644
--- a/server/src/services/authService.ts
+++ b/server/src/services/authService.ts
@@ -15,6 +15,7 @@ import { decrypt_api_key, maybe_encrypt_api_key, encrypt_api_key } from './apiKe
 import { createEphemeralToken } from './ephemeralTokens';
 import { revokeUserSessions } from '../mcp';
 import { startTripReminders } from '../scheduler';
+import { deleteUserCompletely } from './userCleanupService';
 import { verifyJwtAndLoadUser } from '../middleware/auth';
 import { User } from '../types';
 import { DEMO_EMAIL_PRIMARY, isDemoEmail } from './demo';
@@ -527,7 +528,7 @@ export function deleteAccount(userId: number, userEmail: string, userRole: strin
       return { error: 'Cannot delete the last admin account', status: 400 };
     }
   }
-  db.prepare('DELETE FROM users WHERE id = ?').run(userId);
+  deleteUserCompletely(userId);
   return { success: true };
 }
 
diff --git a/server/src/services/userCleanupService.ts b/server/src/services/userCleanupService.ts
new file mode 100644
index 00000000..84239449
--- /dev/null
+++ b/server/src/services/userCleanupService.ts
@@ -0,0 +1,21 @@
+import { db } from '../db/database';
+
+function cleanupUserReferences(userId: number): void {
+  db.prepare('UPDATE trip_members SET invited_by = NULL WHERE invited_by = ?').run(userId);
+  db.prepare('UPDATE budget_items SET paid_by_user_id = NULL WHERE paid_by_user_id = ?').run(userId);
+  db.prepare('DELETE FROM share_tokens WHERE created_by = ?').run(userId);
+  db.prepare('DELETE FROM journey_share_tokens WHERE created_by = ?').run(userId);
+  // Owned journeys cascade-delete their entries/contributors/share_tokens/photos via journey_id FKs
+  db.prepare('DELETE FROM journeys WHERE user_id = ?').run(userId);
+  // Entries authored on other users' journeys (not covered by the cascade above)
+  db.prepare('DELETE FROM journey_entries WHERE author_id = ?').run(userId);
+  db.prepare('DELETE FROM journey_contributors WHERE user_id = ?').run(userId);
+}
+
+export function deleteUserCompletely(userId: number): void {
+  const tx = db.transaction((id: number) => {
+    cleanupUserReferences(id);
+    db.prepare('DELETE FROM users WHERE id = ?').run(id);
+  });
+  tx(userId);
+}
diff --git a/server/tests/integration/admin.test.ts b/server/tests/integration/admin.test.ts
index 0d105c61..541b8035 100644
--- a/server/tests/integration/admin.test.ts
+++ b/server/tests/integration/admin.test.ts
@@ -41,7 +41,7 @@ import { createApp } from '../../src/app';
 import { createTables } from '../../src/db/schema';
 import { runMigrations } from '../../src/db/migrations';
 import { resetTestDb } from '../helpers/test-db';
-import { createUser, createAdmin, createInviteToken } from '../helpers/factories';
+import { createUser, createAdmin, createInviteToken, createTrip, createBudgetItem, createJourney, createJourneyEntry, addJourneyContributor } from '../helpers/factories';
 import { authCookie } from '../helpers/auth';
 import { loginAttempts, mfaAttempts } from '../../src/routes/auth';
 
@@ -148,6 +148,70 @@ describe('Admin user management', () => {
     expect(deleted).toBeUndefined();
   });
 
+  it('ADMIN-005b — DELETE /admin/users/:id succeeds when user has FK references', async () => {
+    const { user: admin } = createAdmin(testDb);
+    const { user: target } = createUser(testDb);
+    const { user: otherUser } = createUser(testDb);
+    const { user: thirdUser } = createUser(testDb);
+
+    // trip_members.invited_by: target invited thirdUser to otherUser's trip
+    // (trip survives deletion; only invited_by should become NULL)
+    const otherTrip = createTrip(testDb, otherUser.id);
+    testDb.prepare('INSERT INTO trip_members (trip_id, user_id, invited_by) VALUES (?, ?, ?)').run(otherTrip.id, thirdUser.id, target.id);
+
+    // share_tokens.created_by: target created a share token for otherUser's trip
+    testDb.prepare("INSERT INTO share_tokens (trip_id, token, created_by) VALUES (?, 'tok-admin-test', ?)").run(otherTrip.id, target.id);
+
+    // budget_items.paid_by_user_id: target paid for an expense on otherUser's trip
+    const budgetItem = createBudgetItem(testDb, otherTrip.id);
+    testDb.prepare('UPDATE budget_items SET paid_by_user_id = ? WHERE id = ?').run(target.id, budgetItem.id);
+
+    // journey_contributors: target is a contributor on otherUser's journey
+    const otherJourney = createJourney(testDb, otherUser.id);
+    addJourneyContributor(testDb, otherJourney.id, target.id);
+
+    // journey_entries: target authored an entry on otherUser's journey
+    createJourneyEntry(testDb, otherJourney.id, target.id);
+
+    // journey_share_tokens: target created a share token for otherUser's journey
+    testDb.prepare("INSERT INTO journey_share_tokens (journey_id, token, created_by) VALUES (?, 'jst-admin-test', ?)").run(otherJourney.id, target.id);
+
+    // notifications.sender_id (SET NULL): target sent a notification to otherUser
+    const sentNotif = testDb.prepare(
+      "INSERT INTO notifications (type, scope, target, sender_id, recipient_id, title_key, text_key) VALUES ('simple', 'trip', ?, ?, ?, 'k', 'k')"
+    ).run(otherTrip.id, target.id, otherUser.id);
+    // notifications.recipient_id (CASCADE): otherUser sent a notification to target
+    testDb.prepare(
+      "INSERT INTO notifications (type, scope, target, sender_id, recipient_id, title_key, text_key) VALUES ('simple', 'trip', ?, ?, ?, 'k', 'k')"
+    ).run(otherTrip.id, otherUser.id, target.id);
+
+    // user_notice_dismissals (CASCADE): target dismissed a notice
+    testDb.prepare(
+      "INSERT INTO user_notice_dismissals (user_id, notice_id, dismissed_at) VALUES (?, 'test-notice', ?)"
+    ).run(target.id, Date.now());
+
+    const res = await request(app)
+      .delete(`/api/admin/users/${target.id}`)
+      .set('Cookie', authCookie(admin.id));
+    expect(res.status).toBe(200);
+    expect(res.body.success).toBe(true);
+
+    expect(testDb.prepare('SELECT id FROM users WHERE id = ?').get(target.id)).toBeUndefined();
+    // trip_members row survives but invited_by is now NULL
+    expect((testDb.prepare('SELECT invited_by FROM trip_members WHERE trip_id = ? AND user_id = ?').get(otherTrip.id, thirdUser.id) as any).invited_by).toBeNull();
+    expect(testDb.prepare('SELECT id FROM share_tokens WHERE created_by = ?').get(target.id)).toBeUndefined();
+    expect((testDb.prepare('SELECT paid_by_user_id FROM budget_items WHERE id = ?').get(budgetItem.id) as any).paid_by_user_id).toBeNull();
+    expect(testDb.prepare('SELECT user_id FROM journey_contributors WHERE journey_id = ? AND user_id = ?').get(otherJourney.id, target.id)).toBeUndefined();
+    expect(testDb.prepare('SELECT id FROM journey_entries WHERE author_id = ?').get(target.id)).toBeUndefined();
+    expect(testDb.prepare('SELECT id FROM journey_share_tokens WHERE created_by = ?').get(target.id)).toBeUndefined();
+    // sent notification survives but sender_id becomes NULL
+    expect((testDb.prepare('SELECT sender_id FROM notifications WHERE id = ?').get(sentNotif.lastInsertRowid) as any).sender_id).toBeNull();
+    // received notification is cascade-deleted
+    expect(testDb.prepare('SELECT id FROM notifications WHERE recipient_id = ?').get(target.id)).toBeUndefined();
+    // notice dismissals are cascade-deleted
+    expect(testDb.prepare("SELECT user_id FROM user_notice_dismissals WHERE user_id = ? AND notice_id = 'test-notice'").get(target.id)).toBeUndefined();
+  });
+
   it('ADMIN-006 — admin cannot delete their own account', async () => {
     const { user: admin } = createAdmin(testDb);
 
diff --git a/server/tests/integration/auth.test.ts b/server/tests/integration/auth.test.ts
index deb9df5a..2ec4571d 100644
--- a/server/tests/integration/auth.test.ts
+++ b/server/tests/integration/auth.test.ts
@@ -52,7 +52,7 @@ import { createApp } from '../../src/app';
 import { createTables } from '../../src/db/schema';
 import { runMigrations } from '../../src/db/migrations';
 import { resetTestDb } from '../helpers/test-db';
-import { createUser, createAdmin, createUserWithMfa, createInviteToken } from '../helpers/factories';
+import { createUser, createAdmin, createUserWithMfa, createInviteToken, createTrip, createBudgetItem, createJourney, createJourneyEntry, addJourneyContributor } from '../helpers/factories';
 import { authCookie, authHeader } from '../helpers/auth';
 import { loginAttempts, mfaAttempts } from '../../src/routes/auth';
 
@@ -509,6 +509,79 @@ describe('Extended auth scenarios', () => {
   });
 });
 
+// ─────────────────────────────────────────────────────────────────────────────
+// Account deletion
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe('Account deletion', () => {
+  it('AUTH-040 — DELETE /auth/me succeeds when user has FK references', async () => {
+    const { user: admin } = createAdmin(testDb);
+    const { user: target } = createUser(testDb);
+    const { user: otherUser } = createUser(testDb);
+    const { user: thirdUser } = createUser(testDb);
+
+    // trip_members.invited_by: target invited thirdUser to otherUser's trip
+    // (trip survives deletion; only invited_by should become NULL)
+    const otherTrip = createTrip(testDb, otherUser.id);
+    testDb.prepare('INSERT INTO trip_members (trip_id, user_id, invited_by) VALUES (?, ?, ?)').run(otherTrip.id, thirdUser.id, target.id);
+
+    // share_tokens.created_by: target created a share token for otherUser's trip
+    testDb.prepare("INSERT INTO share_tokens (trip_id, token, created_by) VALUES (?, 'tok-auth-test', ?)").run(otherTrip.id, target.id);
+
+    // budget_items.paid_by_user_id: target paid for an expense on otherUser's trip
+    const budgetItem = createBudgetItem(testDb, otherTrip.id);
+    testDb.prepare('UPDATE budget_items SET paid_by_user_id = ? WHERE id = ?').run(target.id, budgetItem.id);
+
+    // journey_contributors: target is a contributor on otherUser's journey
+    const otherJourney = createJourney(testDb, otherUser.id);
+    addJourneyContributor(testDb, otherJourney.id, target.id);
+
+    // journey_entries: target authored an entry on otherUser's journey
+    createJourneyEntry(testDb, otherJourney.id, target.id);
+
+    // journey_share_tokens: target created a share token for otherUser's journey
+    testDb.prepare("INSERT INTO journey_share_tokens (journey_id, token, created_by) VALUES (?, 'jst-auth-test', ?)").run(otherJourney.id, target.id);
+
+    // notifications.sender_id (SET NULL): target sent a notification to otherUser
+    const sentNotif = testDb.prepare(
+      "INSERT INTO notifications (type, scope, target, sender_id, recipient_id, title_key, text_key) VALUES ('simple', 'trip', ?, ?, ?, 'k', 'k')"
+    ).run(otherTrip.id, target.id, otherUser.id);
+    // notifications.recipient_id (CASCADE): otherUser sent a notification to target
+    testDb.prepare(
+      "INSERT INTO notifications (type, scope, target, sender_id, recipient_id, title_key, text_key) VALUES ('simple', 'trip', ?, ?, ?, 'k', 'k')"
+    ).run(otherTrip.id, otherUser.id, target.id);
+
+    // user_notice_dismissals (CASCADE): target dismissed a notice
+    testDb.prepare(
+      "INSERT INTO user_notice_dismissals (user_id, notice_id, dismissed_at) VALUES (?, 'test-notice', ?)"
+    ).run(target.id, Date.now());
+
+    // admin exists to ensure target (non-admin user) passes the last-admin guard
+    void admin;
+
+    const res = await request(app)
+      .delete('/api/auth/me')
+      .set('Cookie', authCookie(target.id));
+    expect(res.status).toBe(200);
+    expect(res.body.success).toBe(true);
+
+    expect(testDb.prepare('SELECT id FROM users WHERE id = ?').get(target.id)).toBeUndefined();
+    // trip_members row survives but invited_by is now NULL
+    expect((testDb.prepare('SELECT invited_by FROM trip_members WHERE trip_id = ? AND user_id = ?').get(otherTrip.id, thirdUser.id) as any).invited_by).toBeNull();
+    expect(testDb.prepare('SELECT id FROM share_tokens WHERE created_by = ?').get(target.id)).toBeUndefined();
+    expect((testDb.prepare('SELECT paid_by_user_id FROM budget_items WHERE id = ?').get(budgetItem.id) as any).paid_by_user_id).toBeNull();
+    expect(testDb.prepare('SELECT user_id FROM journey_contributors WHERE journey_id = ? AND user_id = ?').get(otherJourney.id, target.id)).toBeUndefined();
+    expect(testDb.prepare('SELECT id FROM journey_entries WHERE author_id = ?').get(target.id)).toBeUndefined();
+    expect(testDb.prepare('SELECT id FROM journey_share_tokens WHERE created_by = ?').get(target.id)).toBeUndefined();
+    // sent notification survives but sender_id becomes NULL
+    expect((testDb.prepare('SELECT sender_id FROM notifications WHERE id = ?').get(sentNotif.lastInsertRowid) as any).sender_id).toBeNull();
+    // received notification is cascade-deleted
+    expect(testDb.prepare('SELECT id FROM notifications WHERE recipient_id = ?').get(target.id)).toBeUndefined();
+    // notice dismissals are cascade-deleted
+    expect(testDb.prepare("SELECT user_id FROM user_notice_dismissals WHERE user_id = ? AND notice_id = 'test-notice'").get(target.id)).toBeUndefined();
+  });
+});
+
 // ─────────────────────────────────────────────────────────────────────────────
 // Rate limiting (AUTH-004, AUTH-018) — placed last
 // ─────────────────────────────────────────────────────────────────────────────