BehçetDisease (BD) is a systemic vasculitis characterized by recurrent oral and genital ulcers and uveitis, arthritis, and involvement of the gastrointestinal tract, central nervous system and blood vessels. The aneurysms of the pulmonary arteries, with or without thrombosis, are typical manifestation of BD. We report a case with BD, pulmonary arterial aneurysms(PAA) and in situ thrombosis. We aimed to show the effectiveness of immunosuppressive treatment on in situ thrombosis in a case with PAA and BD.