Out of 196 patients with Behçet's disease, 12 (10 men and 2 women, mean age 34 +/- 7 years) had non-coronary arterial lesions. Behçet's disease was complete in 4 patients. The arterial lesions had appeared 8.6 +/- 8 years on average (20 years at most) after the first sign of the disease. Three patients showed evidence of stenosis or occlusion involving one or several arteries. Eight patients had both stenotic and aneurysmal lesions. One patient had an arteriovenous fistula. Another developed a false aneurysm at the site of introduction of a femoral catheter. Yet another patient developed an anastomotic aneurysm one year after implantation of an abdominal aortic graft. In 2 cases histology showed fragmentation of the media associated with vasculitis of the vasa vasorum. Two patients with pulmonary aneurysm died of massive haemoptysis. In 2 patients combined corticosteroid and cyclophosphamide therapy failed to prevent the development of aneurysmal lesions. Phlebitis was associated with arterial involvement in 7 patients. Comparison between patients with or without arterial lesions showed no significant difference in time of onset of Behçet's disease, sex, main clinical features and presence of HLA B5. Aneurysmal lesions respond poorly to medical treatment, and surgery is mandatory. Since recurrence at the site of anastomosis is possible, prolonged monitoring is required.