diff --git a/expiringdict/__init__.py b/expiringdict/__init__.py
index 3e2f298..8056fe0 100644
--- a/expiringdict/__init__.py
+++ b/expiringdict/__init__.py
@@ -26,7 +26,7 @@
 
 
 class ExpiringDict(OrderedDict):
-    def __init__(self, max_len, max_age_seconds):
+    def __init__(self, max_len, max_age_seconds, callback=None):
         assert max_age_seconds >= 0
         assert max_len >= 1
 
@@ -34,6 +34,7 @@ def __init__(self, max_len, max_age_seconds):
         self.max_len = max_len
         self.max_age = max_age_seconds
         self.lock = RLock()
+        self.callback = callback
 
     def __contains__(self, key):
         """ Return True if the dict has a key, else return False. """
@@ -43,6 +44,8 @@ def __contains__(self, key):
                 if time.time() - item[1] < self.max_age:
                     return True
                 else:
+                    if self.callback:
+                        self.callback(item[0])
                     del self[key]
         except KeyError:
             pass
@@ -62,6 +65,8 @@ def __getitem__(self, key, with_age=False):
                 else:
                     return item[0]
             else:
+                if self.callback:
+                    self.callback(item[0])
                 del self[key]
                 raise KeyError(key)