diff --git a/lemon/smart_graph.h b/lemon/smart_graph.h
--- a/lemon/smart_graph.h
+++ b/lemon/smart_graph.h
@@ -194,6 +194,8 @@
   ///Most of its member functions and nested classes are documented
   ///only in the concept class.
   ///
+  ///This class provides constant time counting for nodes and arcs.
+  ///
   ///\sa concepts::Digraph
   ///\sa SmartGraph
   class SmartDigraph : public ExtendedSmartDigraphBase {
@@ -620,6 +622,8 @@
   /// Most of its member functions and nested classes are documented
   /// only in the concept class.
   ///
+  /// This class provides constant time counting for nodes, edges and arcs.
+  ///
   /// \sa concepts::Graph
   /// \sa SmartDigraph
   class SmartGraph : public ExtendedSmartGraphBase {