Behçet's disease (BD) affects the lung as well as the intestine, central nervous system, kidney, and other organs. Pulmonary vasculitis is one of the most severe complications in BD because it can cause fatal bleeding. Corticosteroids and other immunosuppressive drugs have been used to treat pulmonary vasculitis, but the efficacy of these agents has not yet been established. We administered FK506, a novel immunosuppressive agent, as a treatment for BD. A 21-year-old woman presented definitive symptoms of BD, ie, repeated oral and genital ulcers, folliculitis, and panuveitis. The patient showed localized pulmonary infiltrates on her chest x-ray film that were histologically proved to be venulitis consistent with BD. These pulmonary infiltrates evanesced after the oral administration of FK506 for 8 weeks; in addition, the skin lesions and uveitis improved. This clinical observation indicates that FK506 is an effective agent in the treatment of pulmonary vasculitis associated with BD.