The pathogenesis of vascular damage in Behçet's disease (BD) is still unknown. We investigated anticardiolipin antibodies (AC) in a genetically homogeneous group of Italian patients with BD and retinal vasculitis. In a subset, we examined the level of factor VIII-related antigen and antiendothelial cell antibodies (AECA). We found a high prevalence of AC; AECA were not found in most of our patients. Only three patients had raised levels of factor VIII-related antigen, all of whom had systemic involvement. We believe BD may be considered as a vasculitis of unknown origin in which several and different pathogenetic factors may play a role.