Behçet's syndrome is a disease of unknown aetiology classified among the vasculitides. It runs a course of exacerbations and remissions which gradually abate with time. Eye disease, the most frequent cause of serious morbidity, may lead to blindness in 20% of those affected. The syndrome may occasionally be fatal due to vasculitis leading to arterial occlusion, ruptured arterial aneurysms or pulmonary vasculitis, or involvement of the central nervous system. Immunosuppressive drugs have been shown to be moderately successful in inducing and maintaining remissions. Azathioprine at a dose of 2.5 mg/kg/day has been shown to control the progression of existing, and the development of new, eye disease. Cyclosporin A is also beneficial in controlling active eye disease and although it has a more rapid action than azathioprine, its toxicity limits its long term use. Colchicine, although widely prescribed, has been shown in a controlled trial to be effective only in reducing the development of erythema nodosum and arthralgia. Systemic corticosteroids, once widely used, are now reserved only for the most severe cases of inflammatory eye disease and vasculitis, where they are frequently used as intravenous pulse therapy. Local mydriatics are used to prevent synechiae. Local treatment with corticosteroids, sometimes in conjunction with antibiotics, control oral and genital ulcers which may also be controlled by immunosuppressives, which are reserved for the most severe cases. Thrombophlebitis usually only requires antiplatelet agents, whereas arteritis is treated conventionally with a combination of corticosteroids and immunosuppressive drugs, usually cyclophosphamide.