diff --git a/src/client/stdio.test.ts b/src/client/stdio.test.ts
index 646f9ea5..b2132446 100644
--- a/src/client/stdio.test.ts
+++ b/src/client/stdio.test.ts
@@ -59,3 +59,12 @@ test("should read messages", async () => {
 
   await client.close();
 });
+
+test("should return child process pid", async () => {
+  const client = new StdioClientTransport(serverParameters);
+
+  await client.start();
+  expect(client.pid).not.toBeNull();
+  await client.close();
+  expect(client.pid).toBeNull();
+});
diff --git a/src/client/stdio.ts b/src/client/stdio.ts
index 9e35293d..af29614e 100644
--- a/src/client/stdio.ts
+++ b/src/client/stdio.ts
@@ -184,6 +184,15 @@ export class StdioClientTransport implements Transport {
     return this._process?.stderr ?? null;
   }
 
+  /**
+   * The child process pid spawned by this transport.
+   *
+   * This is only available after the transport has been started.
+   */
+  get pid(): number | null {
+    return this._process?.pid ?? null;
+  }
+
   private processReadBuffer() {
     while (true) {
       try {