Using boost 1_41 I found what I believe to be a bug in is_virtual_base_of. The following code reports that A and B are both virtual base classes of C. #include<boost/type_traits/is_virtual_base_of.hpp> #include <stdio.h> struct A { int base_old; }; struct B { int base_data; }; struct C : public A, public B { virtual void test(){}; float my_data; }; int main ( int argc, char** argv ) { printf( "is_virtual_base_of<A,C>::value: %d\n", boost::is_virtual_base_of<A,C>::value ); printf( "is_virtual_base_of<B,C>::value: %d\n", boost::is_virtual_base_of<B,C>::value ); } i686-apple-darwin10-g++-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5646) (dot 1) Copyright (C) 2007 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.