A 71-year-old man was operated for a complete occlusion of the left common iliac artery caused by arteriosclerosis obliterans. Cross-over bypass was performed from the right external iliac artery to the left superficial femoral artery in June 1978, using a Double Velour Dacron graft (Cooley) 8 mm in diameter. In February 1985, the patient noticed the pulsatile mass in his left groin. Angiography showed a false aneurysm at the distal anastomosis of the graft. On operation, 2 aneurysmal dilatations were found on the distal anastomosis. After resection of the aneurysms, the reconstruction was established by EPTFE graft successfully. The resected specimen showed that one of the aneurysms was caused by the anastomotic failure of the distal portion of the graft, but that the other was the false aneurysm caused by rupture of the implanted graft. Two ruptured holes were confirmed to be 20 X 25 mm, 10 X 15 mm in size respectively, 10 mm proximal to the anastomotic aneurysm. Rupture of the Dacron arterial prosthesis is a rare complication. Only 23 cases have been reported in the United States. But some literatures show that the incidence of the failure of the Dacron prosthesis was about 3%. Therefore, we should make a long-term follow-up to the patients implanted Dacron arterial prostheses.