Behçet's disease is a systemic vasculitis of unknown aetiology characteristically affecting venules. Onset is typically in young adults with recurrent oral and genital ulceration, uveitis, skin manifestations, arthritis, neurological involvement, and a tendency to thrombosis. It has a worldwide distribution but is prevalent in Japan, the Middle East, and some Mediterranean countries. International diagnostic criteria have been proposed, however diagnosis can be problematical, particularly if the typical ulcers are not obvious at presentation. Treatment is challenging, must be tailored to the pattern of organ involvement for each patient and often requires combination therapies.