diff --git a/changelog.d/327.bugfix.rst b/changelog.d/327.bugfix.rst
new file mode 100644
index 00000000..e6391df7
--- /dev/null
+++ b/changelog.d/327.bugfix.rst
@@ -0,0 +1 @@
+``treq.testing.StubTreq`` now persists ``twisted.web.server.Session`` instances between requests.
diff --git a/docs/testing.rst b/docs/testing.rst
index 2f292b51..855bc69c 100644
--- a/docs/testing.rst
+++ b/docs/testing.rst
@@ -57,3 +57,4 @@ This is superior to calling your resource's methods directly or passing mock obj
 Thus, the ``request`` object your code interacts with is a *real* :class:`twisted.web.server.Request` and behaves the same as it would in production.
 
 Note that if your resource returns :data:`~twisted.web.server.NOT_DONE_YET` you must keep a reference to the :class:`~treq.testing.RequestTraversalAgent` and call its :meth:`~treq.testing.RequestTraversalAgent.flush()` method to spin the memory reactor once the server writes additional data before the client will receive it.
+
diff --git a/src/treq/test/test_testing.py b/src/treq/test/test_testing.py
index eb804158..1615472a 100644
--- a/src/treq/test/test_testing.py
+++ b/src/treq/test/test_testing.py
@@ -52,6 +52,34 @@ def render(self, request):
         return NOT_DONE_YET
 
 
+class _SessionIdTestResource(Resource):
+    """
+    Resource that returns the current session ID.
+    """
+    isLeaf = True
+
+    def __init__(self):
+        super().__init__()
+        # keep track of all sessions created, so we can manually expire them later
+        self.sessions = []
+
+    def render(self, request):
+        session = request.getSession()
+        if session not in self.sessions:
+            # new session, add to internal list
+            self.sessions.append(session)
+        uid = session.uid
+        return uid
+
+    def expire_sessions(self):
+        """
+        Manually expire all sessions created by this resource.
+        """
+        for session in self.sessions:
+            session.expire()
+        self.sessions = []
+
+
 class StubbingTests(TestCase):
     """
     Tests for :class:`StubTreq`.
@@ -242,6 +270,40 @@ def test_handles_successful_asynchronous_requests_with_streaming(self):
         stub.flush()
         self.successResultOf(d)
 
+    def test_session_persistence_between_requests(self):
+        """
+        Calling request.getSession() in the wrapped resource will return
+        a session with the same ID, until the sessions are cleaned.
+        """
+        rsrc = _SessionIdTestResource()
+        stub = StubTreq(rsrc)
+        # request 1, getting original session ID
+        d = stub.request("method", "http://example.com/")
+        resp = self.successResultOf(d)
+        cookies = resp.cookies()
+        sid_1 = self.successResultOf(resp.content())
+        # request 2, ensuring session ID stays the same
+        d = stub.request("method", "http://example.com/", cookies=cookies)
+        resp = self.successResultOf(d)
+        sid_2 = self.successResultOf(resp.content())
+        self.assertEqual(sid_1, sid_2)
+        # request 3, ensuring the session IDs are different after cleaning
+        # or expiring the sessions
+
+        # manually expire the sessions.
+        rsrc.expire_sessions()
+
+        d = stub.request("method", "http://example.com/")
+        resp = self.successResultOf(d)
+        cookies = resp.cookies()
+        sid_3 = self.successResultOf(resp.content())
+        self.assertNotEqual(sid_1, sid_3)
+        # request 4, ensuring that once again the session IDs are the same
+        d = stub.request("method", "http://example.com/", cookies=cookies)
+        resp = self.successResultOf(d)
+        sid_4 = self.successResultOf(resp.content())
+        self.assertEqual(sid_3, sid_4)
+
 
 class HasHeadersTests(TestCase):
     """
diff --git a/src/treq/testing.py b/src/treq/testing.py
index df633beb..33d8c94d 100644
--- a/src/treq/testing.py
+++ b/src/treq/testing.py
@@ -26,7 +26,7 @@
 from twisted.web.error import SchemeNotSupported
 from twisted.web.iweb import IAgent, IAgentEndpointFactory, IBodyProducer
 from twisted.web.resource import Resource
-from twisted.web.server import Site
+from twisted.web.server import Session, Site
 
 from zope.interface import directlyProvides, implementer
 
@@ -88,6 +88,12 @@ def __init__(self, rootResource):
             reactor=self._memoryReactor,
             endpointFactory=_EndpointFactory(self._memoryReactor))
         self._rootResource = rootResource
+        self._serverFactory = Site(self._rootResource, reactor=self._memoryReactor)
+        self._serverFactory.sessionFactory = lambda site, uid: Session(
+            site,
+            uid,
+            reactor=self._memoryReactor,
+        )
         self._pumps = set()
 
     def request(self, method, uri, headers=None, bodyProducer=None):
@@ -126,8 +132,7 @@ def check_already_called(r):
         # Create the protocol and fake transport for the client and server,
         # using the factory that was passed to the MemoryReactor for the
         # client, and a Site around our rootResource for the server.
-        serverFactory = Site(self._rootResource, reactor=self._memoryReactor)
-        serverProtocol = serverFactory.buildProtocol(clientAddress)
+        serverProtocol = self._serverFactory.buildProtocol(clientAddress)
         serverTransport = iosim.FakeTransport(
             serverProtocol, isServer=True,
             hostAddress=serverAddress, peerAddress=clientAddress)
@@ -228,8 +233,8 @@ def __init__(self, resource):
         :param resource: A :obj:`Resource` object that provides the fake
             responses
         """
-        _agent = RequestTraversalAgent(resource)
-        _client = HTTPClient(agent=_agent,
+        self._agent = RequestTraversalAgent(resource)
+        _client = HTTPClient(agent=self._agent,
                              data_to_body_producer=_SynchronousProducer)
         for function_name in treq.__all__:
             function = getattr(_client, function_name, None)
@@ -239,7 +244,7 @@ def __init__(self, resource):
                 function = _reject_files(function)
 
             setattr(self, function_name, function)
-        self.flush = _agent.flush
+        self.flush = self._agent.flush
 
 
 class StringStubbingResource(Resource):