I am sometimes getting segmentation faults (using gcc 3.3.4 under Cygwin) in calls to add_vertex( g ), where g is of the following type: boost::adjacency_list < boost::setS, boost::vecS, boost::undirectedS, Vertex_Properties, Edge_Length > This happens when I try to merge two graphs with repeated calls to add_vertex (not updating edges or anything, just adding new vertices), and usually when the returned index from add_vertex is around 40000-50000, but it depends on the data. Creating a single graph with more than 50000 vertices in one go is not a problem. Does anyone have an idea of what is going on in add_vertex, and what could be the problem here? I suspect it has something to do with the automatic resizing of the internal vector used to store the vertices. Is there a way to reserve memory in advance for this?