We herein describe a patient with Behçet's disease in whom we followed the development and resolution of pulmonary artery aneurysms. He presented with intermittent hemoptysis, pulmonary thromboembolism was initially diagnosed, and anticoagulant therapy was started. Over the next several months, the expansion of pulmonary arteries was noted. Five months after his initial admission, he was readmitted for massive hemoptysis, and further examinations revealed that he had Behçet's disease. Corticosteroids and intravenous cyclophosphamide were started. Over the next five months, the pulmonary artery aneurysms and thrombosis resolved. The development of pulmonary artery aneurysms led to the diagnosis of Behçet's disease, and they resolved after immunosuppressive therapy.