diff --git a/tildes/tildes/metrics.py b/tildes/tildes/metrics.py
index 87184ae..71adf54 100644
--- a/tildes/tildes/metrics.py
+++ b/tildes/tildes/metrics.py
@@ -31,6 +31,9 @@ _COUNTERS = {
     "login_failures": Counter("tildes_login_failures_total", "Login Failures"),
     "messages": Counter("tildes_messages_total", "Messages", labelnames=["type"]),
     "registrations": Counter("tildes_registrations_total", "User Registrations"),
+    "theme_cookie_tween_sets": Counter(
+        "tildes_theme_cookie_tween_sets_total", "Theme Cookies Set by Tween"
+    ),
     "topics": Counter("tildes_topics_total", "Topics", labelnames=["type"]),
     "subscriptions": Counter("tildes_subscriptions_total", "Subscriptions"),
     "unsubscriptions": Counter("tildes_unsubscriptions_total", "Unsubscriptions"),
diff --git a/tildes/tildes/tweens.py b/tildes/tildes/tweens.py
index 378598c..c49e8e1 100644
--- a/tildes/tildes/tweens.py
+++ b/tildes/tildes/tweens.py
@@ -11,6 +11,8 @@ from pyramid.registry import Registry
 from pyramid.request import Request
 from pyramid.response import Response
 
+from tildes.metrics import incr_counter
+
 
 def http_method_tween_factory(handler: Callable, registry: Registry) -> Callable:
     # pylint: disable=unused-argument
@@ -95,6 +97,8 @@ def theme_cookie_tween_factory(handler: Callable, registry: Registry) -> Callabl
                 secure=True,
                 domain="." + request.domain,
             )
+            incr_counter("theme_cookie_tween_sets")
+
         return response
 
     return theme_cookie_tween