Vascular involvement in Behçet's disease is rare and may cause life-threatening complications. We report on 3 patients who presented with vascular problems in the course of the illness. (1) A 37-year-old woman suffered multiple pulmonary artery aneurysms (PAA) 3 years after the first symptoms of Behçet's disease (BD) had been noted. They completely regressed under three-month high-dose corticosteroid therapy and remission has lasted now for 2 years. (2) The second patient, a 22-year-old man, developed 2 vascular complications of BD: first (1986-1987), he was shown to have a sinus venous thrombosis which resolved under prednisone and oral anticoagulation therapy. Then (1988) he presented with multiple large PAA and high fever. Despite marked radiological regression of the multiple PAA under high-dose prednisone treatment, he remained symptomatic. Repeated hemoptysis in September 1988 prompted us to add cyclosporine A in a dosage providing whole blood levels of 250-350 ng/ml. Four months later pulmonary radiological studies had normalized, but manifestations of BD on the skin and mucosa remained unchanged. 7 months after starting Cy A therapy the patient died suddenly of massive hemoptysis. (3) The third patient, a 23-year-old Spanish immigrant, had a diagnosis of BD when presenting with sinus thrombosis. Later he underwent surgery 3 times for false aneurysms of the common femoral artery which developed at the site where he had been punctured for angiography.(ABSTRACT TRUNCATED AT 250 WORDS)