If you have set a callback to occur when a cached item is removed, you will be provided with a CacheItemRemovedReason argument. The CacheItemRemovedReason will be Expired if the sliding or absolute expiration time interval passed, Removed if the object was removed programmatically with the Cache.Remove( ) method or by an Cache.Insert( ) method with the same key, DependencyChanged if the object was invalidated because of a dependency, or Underused if it has been removed to free memory.