Two patients with Behĉet's disease are reported, both of whom had aneurysms of peripheral arteries. In one the aneurysms were multiple. The aneurysm was replaced with a Terylene prosthesis in one patient, and in the other an autogenous vein bypass was used. In each case a further aneurysm developed adjacent to the vascular anastomosis. Severe ischaemia of the affected limbs subsequently developed in both patients.