Behçet's disease is a systemic inflammatory disorder capable of inducing thrombophlebitis. Clinicopathologically, it is characterized by neutrophil and platelet hyperfunction. Lesions are formed presumably because neutrophils infiltrating the affected tissue release active oxygen and lysosomal enzymes in large amounts. The mechanism of neutrophil hyperfunction was obscure, but in recent years attention has focused on the effects of cytokines released by mononuclear cells. As more has been learned about the etiopathogenesis of Behçet's disease, novel anti-inflammatory drugs, immunosuppressants, anti-thrombotic agents, and anticoagulants have helped to achieve remarkable progress in treatment. Particularly notable is the effect on severe uveitis of cyclosporine, which is more effective than colchicine and conventional immunosuppressants. With the advent of cyclosporine, the number of patients with Behçet's disease who lose their eyesight has clearly decreased.