diff --git a/pyproject.toml b/pyproject.toml
index 02a3820fc..df32ce2a1 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -81,6 +81,7 @@ filterwarnings = [
     "error",
     "ignore: run_until_first_complete is deprecated and will be removed in a future version.:DeprecationWarning",
     "ignore: starlette.middleware.wsgi is deprecated and will be removed in a future release.*:DeprecationWarning",
+    "ignore: The `timeout` argument doesn't work, is deprecated, and will be removed in future versions.*:DeprecationWarning",
     "ignore: Async generator 'starlette.requests.Request.stream' was garbage collected before it had been exhausted.*:ResourceWarning",
     "ignore: Use 'content=<...>' to upload raw bytes/text content.:DeprecationWarning",
 ]
diff --git a/starlette/testclient.py b/starlette/testclient.py
index fb2ad6e35..2fe9844fc 100644
--- a/starlette/testclient.py
+++ b/starlette/testclient.py
@@ -7,6 +7,7 @@
 import math
 import sys
 import typing
+import warnings
 from concurrent.futures import Future
 from types import GeneratorType
 from urllib.parse import unquote, urljoin
@@ -409,6 +410,17 @@ def _portal_factory(self) -> typing.Generator[anyio.abc.BlockingPortal, None, No
             with anyio.from_thread.start_blocking_portal(**self.async_backend) as portal:
                 yield portal
 
+    def _handle_timeout(
+        self,
+        timeout: httpx._types.TimeoutTypes | None,
+    ) -> httpx._types.TimeoutTypes | httpx._client.UseClientDefault:
+        default_timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT
+        if timeout is not None:
+            message = "The `timeout` argument doesn't work, is deprecated, and will be removed in future versions."
+            warnings.warn(message, DeprecationWarning)
+            return timeout
+        return default_timeout
+
     def request(  # type: ignore[override]
         self,
         method: str,
@@ -423,9 +435,10 @@ def request(  # type: ignore[override]
         cookies: httpx._types.CookieTypes | None = None,
         auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
         follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
-        timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
+        timeout: httpx._types.TimeoutTypes | None = None,
         extensions: dict[str, typing.Any] | None = None,
     ) -> httpx.Response:
+        _timeout = self._handle_timeout(timeout)
         url = self._merge_url(url)
         return super().request(
             method,
@@ -439,7 +452,7 @@ def request(  # type: ignore[override]
             cookies=cookies,
             auth=auth,
             follow_redirects=follow_redirects,
-            timeout=timeout,
+            timeout=_timeout,
             extensions=extensions,
         )
 
@@ -452,9 +465,10 @@ def get(  # type: ignore[override]
         cookies: httpx._types.CookieTypes | None = None,
         auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
         follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
-        timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
+        timeout: httpx._types.TimeoutTypes | None = None,
         extensions: dict[str, typing.Any] | None = None,
     ) -> httpx.Response:
+        _timeout = self._handle_timeout(timeout)
         return super().get(
             url,
             params=params,
@@ -462,7 +476,7 @@ def get(  # type: ignore[override]
             cookies=cookies,
             auth=auth,
             follow_redirects=follow_redirects,
-            timeout=timeout,
+            timeout=_timeout,
             extensions=extensions,
         )
 
@@ -475,9 +489,10 @@ def options(  # type: ignore[override]
         cookies: httpx._types.CookieTypes | None = None,
         auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
         follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
-        timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
+        timeout: httpx._types.TimeoutTypes | None = None,
         extensions: dict[str, typing.Any] | None = None,
     ) -> httpx.Response:
+        _timeout = self._handle_timeout(timeout)
         return super().options(
             url,
             params=params,
@@ -485,7 +500,7 @@ def options(  # type: ignore[override]
             cookies=cookies,
             auth=auth,
             follow_redirects=follow_redirects,
-            timeout=timeout,
+            timeout=_timeout,
             extensions=extensions,
         )
 
@@ -498,9 +513,10 @@ def head(  # type: ignore[override]
         cookies: httpx._types.CookieTypes | None = None,
         auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
         follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
-        timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
+        timeout: httpx._types.TimeoutTypes | None = None,
         extensions: dict[str, typing.Any] | None = None,
     ) -> httpx.Response:
+        _timeout = self._handle_timeout(timeout)
         return super().head(
             url,
             params=params,
@@ -508,7 +524,7 @@ def head(  # type: ignore[override]
             cookies=cookies,
             auth=auth,
             follow_redirects=follow_redirects,
-            timeout=timeout,
+            timeout=_timeout,
             extensions=extensions,
         )
 
@@ -525,9 +541,10 @@ def post(  # type: ignore[override]
         cookies: httpx._types.CookieTypes | None = None,
         auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
         follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
-        timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
+        timeout: httpx._types.TimeoutTypes | None = None,
         extensions: dict[str, typing.Any] | None = None,
     ) -> httpx.Response:
+        _timeout = self._handle_timeout(timeout)
         return super().post(
             url,
             content=content,
@@ -539,7 +556,7 @@ def post(  # type: ignore[override]
             cookies=cookies,
             auth=auth,
             follow_redirects=follow_redirects,
-            timeout=timeout,
+            timeout=_timeout,
             extensions=extensions,
         )
 
@@ -556,9 +573,10 @@ def put(  # type: ignore[override]
         cookies: httpx._types.CookieTypes | None = None,
         auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
         follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
-        timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
+        timeout: httpx._types.TimeoutTypes | None = None,
         extensions: dict[str, typing.Any] | None = None,
     ) -> httpx.Response:
+        _timeout = self._handle_timeout(timeout)
         return super().put(
             url,
             content=content,
@@ -570,7 +588,7 @@ def put(  # type: ignore[override]
             cookies=cookies,
             auth=auth,
             follow_redirects=follow_redirects,
-            timeout=timeout,
+            timeout=_timeout,
             extensions=extensions,
         )
 
@@ -587,9 +605,10 @@ def patch(  # type: ignore[override]
         cookies: httpx._types.CookieTypes | None = None,
         auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
         follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
-        timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
+        timeout: httpx._types.TimeoutTypes | None = None,
         extensions: dict[str, typing.Any] | None = None,
     ) -> httpx.Response:
+        _timeout = self._handle_timeout(timeout)
         return super().patch(
             url,
             content=content,
@@ -601,7 +620,7 @@ def patch(  # type: ignore[override]
             cookies=cookies,
             auth=auth,
             follow_redirects=follow_redirects,
-            timeout=timeout,
+            timeout=_timeout,
             extensions=extensions,
         )
 
@@ -614,9 +633,10 @@ def delete(  # type: ignore[override]
         cookies: httpx._types.CookieTypes | None = None,
         auth: httpx._types.AuthTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
         follow_redirects: bool | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
-        timeout: httpx._types.TimeoutTypes | httpx._client.UseClientDefault = httpx._client.USE_CLIENT_DEFAULT,
+        timeout: httpx._types.TimeoutTypes | None = None,
         extensions: dict[str, typing.Any] | None = None,
     ) -> httpx.Response:
+        _timeout = self._handle_timeout(timeout)
         return super().delete(
             url,
             params=params,
@@ -624,7 +644,7 @@ def delete(  # type: ignore[override]
             cookies=cookies,
             auth=auth,
             follow_redirects=follow_redirects,
-            timeout=timeout,
+            timeout=_timeout,
             extensions=extensions,
         )
 
diff --git a/tests/test_testclient.py b/tests/test_testclient.py
index 478dbca46..a9b0f2482 100644
--- a/tests/test_testclient.py
+++ b/tests/test_testclient.py
@@ -422,3 +422,22 @@ async def app(scope: Scope, receive: Receive, send: Send) -> None:
     with client.websocket_connect("/hello-world", params={"foo": "bar"}) as websocket:
         data = websocket.receive_bytes()
         assert data == b"/hello-world"
+
+
+@pytest.mark.parametrize("method", [None, "GET", "POST", "PUT", "PATCH", "DELETE", "OPTIONS", "HEAD"])
+def test_warning_timeout_deprecation(test_client_factory: TestClientFactory, method: str | None) -> None:
+    def homepage(request: Request) -> Response:
+        return Response("Hello, world!")
+
+    allowed_method = [method] if method else None
+    app = Starlette(routes=[Route("/", endpoint=homepage, methods=allowed_method)])
+    client = test_client_factory(app)
+    with pytest.warns(
+        DeprecationWarning,
+        match="The `timeout` argument doesn't work, is deprecated, and will be removed in future versions.",
+    ):
+        if method is None:
+            client.request("GET", "/", timeout=0.1)
+        else:
+            client_method = getattr(client, method.lower())
+            client_method("/", timeout=0.1)