An analysis is made of 16 false aneurysms occurring after arterial grafting in 14 patients. Eight aneurysms were in the abdomen; six were at anastomotic sites on femoral arteries. One was in the popliteal artery and one at an arteriotomy site in a femoral graft. None was due to infection. Eleven seemed due to weakness of the arterial wall. In five the problem was the lack of strength (silk) or the lack of proper tying (polyethylene) of the suture material. Eleven of the 16 did not present until two years or more after insertion.