diff --git a/src/__tests__/portal.test.ts b/src/__tests__/portal.test.ts
index 73f05ff..7fc32a3 100644
--- a/src/__tests__/portal.test.ts
+++ b/src/__tests__/portal.test.ts
@@ -4,6 +4,7 @@ import { Hono } from "hono";
 const CLIENT_ID = "550e8400-e29b-41d4-a716-446655440001";
 const APPOINTMENT_ID = "660e8400-e29b-41d4-a716-446655440002";
 const SESSION_ID = "770e8400-e29b-41d4-a716-446655440003";
+const PET_ID = "880e8400-e29b-41d4-a716-446655440004";
 
 const futureDate = () => new Date(Date.now() + 30 * 60 * 1000);
 const pastDate = () => new Date(Date.now() - 5 * 60 * 1000);
@@ -37,13 +38,38 @@ const APPOINTMENT = {
   cancelledAt: null,
 };
 
+const PET = {
+  id: PET_ID,
+  clientId: CLIENT_ID,
+  name: "Fido",
+  species: "dog",
+  breed: "Labrador",
+  weightKg: "30.00",
+  dateOfBirth: null,
+  healthAlerts: null,
+  groomingNotes: null,
+  cutStyle: null,
+  shampooPreference: null,
+  specialCareNotes: null,
+  coatType: null,
+  petSizeCategory: null,
+  customFields: {},
+  photoKey: null,
+  photoUploadedAt: null,
+  image: null,
+  createdAt: new Date(),
+  updatedAt: new Date(),
+};
+
 let selectSessionRow: Record<string, unknown> | null = null;
 let selectAppointmentRow: Record<string, unknown> | null = null;
+let selectPetRow: Record<string, unknown> | null = null;
 let updatedValues: Record<string, unknown>[] = [];
 
 function resetMock() {
   selectSessionRow = null;
   selectAppointmentRow = null;
+  selectPetRow = null;
   updatedValues = [];
 }
 
@@ -62,6 +88,8 @@ vi.mock("@groombook/db", () => {
     return chain;
   }
 
+  let activeUpdateTable: string | null = null;
+
   const impersonationSessions = new Proxy(
     { _name: "impersonationSessions" },
     { get: (t, p) => (p === "_name" ? "impersonationSessions" : { table: "impersonationSessions", column: p }) }
@@ -72,6 +100,16 @@ vi.mock("@groombook/db", () => {
     { get: (t, p) => (p === "_name" ? "appointments" : { table: "appointments", column: p }) }
   );
 
+  const pets = new Proxy(
+    { _name: "pets" },
+    { get: (t, p) => (p === "_name" ? "pets" : { table: "pets", column: p }) }
+  );
+
+  const impersonationAuditLogs = new Proxy(
+    { _name: "impersonationAuditLogs" },
+    { get: (t, p) => (p === "_name" ? "impersonationAuditLogs" : { table: "impersonationAuditLogs", column: p }) }
+  );
+
   return {
     getDb: () => ({
       select: () => ({
@@ -82,26 +120,44 @@ vi.mock("@groombook/db", () => {
           if (table._name === "appointments") {
             return makeChainable(selectAppointmentRow ? [selectAppointmentRow] : []);
           }
+          if (table._name === "pets") {
+            return makeChainable(selectPetRow ? [selectPetRow] : []);
+          }
           return makeChainable([]);
         },
       }),
-      update: () => ({
-        set: (vals: Record<string, unknown>) => ({
-          where: () => ({
-            returning: () => {
-              if (selectAppointmentRow) {
-                const updated = { ...selectAppointmentRow, ...vals };
-                updatedValues.push(vals);
-                return [updated];
-              }
-              return [];
-            },
-          }),
+      insert: () => ({
+        values: () => ({
+          returning: () => [{}],
         }),
       }),
+      update: (table: { _name: string }) => {
+        activeUpdateTable = table._name;
+        return {
+          set: (vals: Record<string, unknown>) => ({
+            where: () => ({
+              returning: () => {
+                if (activeUpdateTable === "appointments" && selectAppointmentRow) {
+                  const updated = { ...selectAppointmentRow, ...vals };
+                  updatedValues.push(vals);
+                  return [updated];
+                }
+                if (activeUpdateTable === "pets" && selectPetRow) {
+                  const updated = { ...selectPetRow, ...vals };
+                  updatedValues.push(vals);
+                  return [updated];
+                }
+                return [];
+              },
+            }),
+          }),
+        };
+      },
     }),
     impersonationSessions,
     appointments,
+    pets,
+    impersonationAuditLogs,
     eq: vi.fn(),
     and: vi.fn(),
   };
@@ -420,4 +476,81 @@ describe("POST /portal/appointments/:id/cancel", () => {
     );
     expect(res.status).toBe(404);
   });
+});
+
+// ─── PATCH /portal/pets/:id ───────────────────────────────────────────────────
+
+function jsonPetPatch(path: string, body: unknown, headers?: Record<string, string>) {
+  return app.request(path, {
+    method: "PATCH",
+    headers: {
+      "Content-Type": "application/json",
+      ...headers,
+    },
+    body: JSON.stringify(body),
+  });
+}
+
+describe("PATCH /portal/pets/:id", () => {
+  it("updates a pet and returns the updated pet in portal shape", async () => {
+    selectSessionRow = ACTIVE_SESSION;
+    selectPetRow = { ...PET, dateOfBirth: new Date("2020-01-15"), photoKey: "pets/test.jpg" };
+    const res = await jsonPetPatch(
+      `/portal/pets/${PET_ID}`,
+      { name: "Fido Jr.", groomingNotes: "Needs extra brushing" },
+      { "X-Impersonation-Session-Id": SESSION_ID }
+    );
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body).toHaveProperty("id");
+    expect(body).toHaveProperty("name", "Fido Jr.");
+    expect(body).toHaveProperty("notes", "Needs extra brushing");
+    expect(body).toHaveProperty("breed");
+    expect(body).toHaveProperty("photoUrl");
+    expect(body).not.toHaveProperty("clientId");
+    expect(body).not.toHaveProperty("customFields");
+  });
+
+  it("returns 401 without X-Impersonation-Session-Id header", async () => {
+    const res = await jsonPetPatch(`/portal/pets/${PET_ID}`, { name: "Test" });
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body.error).toBe("Unauthorized");
+  });
+
+  it("returns 401 with expired session", async () => {
+    selectSessionRow = EXPIRED_SESSION;
+    const res = await jsonPetPatch(
+      `/portal/pets/${PET_ID}`,
+      { name: "Test" },
+      { "X-Impersonation-Session-Id": SESSION_ID }
+    );
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body.error).toBe("Unauthorized");
+  });
+
+  it("returns 403 when pet belongs to a different client", async () => {
+    selectSessionRow = { ...ACTIVE_SESSION, clientId: "different-client-id" };
+    selectPetRow = { ...PET };
+    const res = await jsonPetPatch(
+      `/portal/pets/${PET_ID}`,
+      { name: "Hacked" },
+      { "X-Impersonation-Session-Id": SESSION_ID }
+    );
+    expect(res.status).toBe(403);
+    const body = await res.json();
+    expect(body.error).toBe("Forbidden");
+  });
+
+  it("returns 404 when pet not found", async () => {
+    selectSessionRow = ACTIVE_SESSION;
+    selectPetRow = null;
+    const res = await jsonPetPatch(
+      `/portal/pets/nonexistent-id`,
+      { name: "Ghost" },
+      { "X-Impersonation-Session-Id": SESSION_ID }
+    );
+    expect(res.status).toBe(404);
+  });
 });
\ No newline at end of file
diff --git a/src/routes/portal.ts b/src/routes/portal.ts
index a4c2b87..bbbc197 100644
--- a/src/routes/portal.ts
+++ b/src/routes/portal.ts
@@ -152,6 +152,67 @@ portalRouter.get("/pets", async (c) => {
   return c.json(clientPets.map(p => ({ id: p.id, name: p.name, breed: p.breed, weight: p.weightKg, birthDate: p.dateOfBirth, photoUrl: p.photoKey, notes: p.groomingNotes })));
 });
 
+const portalUpdatePetSchema = z.object({
+  name: z.string().min(1).max(200).optional(),
+  species: z.string().min(1).max(100).optional(),
+  breed: z.string().max(200).optional(),
+  weightKg: z.number().positive().optional(),
+  dateOfBirth: z.string().datetime().optional(),
+  healthAlerts: z.string().max(2000).optional(),
+  groomingNotes: z.string().max(2000).optional(),
+  cutStyle: z.string().max(500).optional(),
+  shampooPreference: z.string().max(500).optional(),
+  specialCareNotes: z.string().max(2000).optional(),
+  customFields: z.record(z.string(), z.string()).optional(),
+  petSizeCategory: z.enum(["small", "medium", "large", "extra_large"]).optional(),
+  coatType: z.enum(["short", "medium", "long", "double", "wire", "silky", "curly", "hairless"]).optional(),
+});
+
+portalRouter.patch(
+  "/pets/:id",
+  zValidator("json", portalUpdatePetSchema),
+  async (c) => {
+    const db = getDb();
+    const petId = c.req.param("id");
+    const clientId = c.get("portalClientId");
+    const body = c.req.valid("json");
+
+    const [existing] = await db
+      .select()
+      .from(pets)
+      .where(eq(pets.id, petId))
+      .limit(1);
+
+    if (!existing) return c.json({ error: "Not found" }, 404);
+    if (existing.clientId !== clientId) return c.json({ error: "Forbidden" }, 403);
+
+    const { weightKg, dateOfBirth, customFields, ...rest } = body;
+    const [updated] = await db
+      .update(pets)
+      .set({
+        ...rest,
+        weightKg: weightKg?.toString(),
+        dateOfBirth: dateOfBirth ? new Date(dateOfBirth) : undefined,
+        ...(customFields !== undefined ? { customFields } : {}),
+        updatedAt: new Date(),
+      })
+      .where(eq(pets.id, petId))
+      .returning();
+
+    if (!updated) return c.json({ error: "Not found" }, 404);
+
+    return c.json({
+      id: updated.id,
+      name: updated.name,
+      breed: updated.breed,
+      weight: updated.weightKg,
+      birthDate: updated.dateOfBirth,
+      photoUrl: updated.photoKey,
+      notes: updated.groomingNotes,
+    });
+  }
+);
+
 portalRouter.get("/invoices", async (c) => {
   const db = getDb();
   const clientId = c.get("portalClientId");