In 53 cases of aorto-iliac and 9 cases of femoro-popliteal operations with use of arterial allografts and followed systematically for 15 years, the authors correlated the findings of the clinical course, the angiographic observations, and the results of the histologic study of recovered grafts. During the sixth to the 15th postoperative years, all but one of the nine femoral grafts open at five years postoperatively became occluded and the only remaining patent graft showed degenerative changes. During the same period of observation, among the 53 aorto-iliac grafts open at five years postoperatively, 44 remained open for various lengths of time and at the 15th postoperative year 18 were still patent. Fourteen of the aortic grafts developed aneurysms, nine of which were replaced; three patients lost their lives due to complications of secondary aneurysms in the grafts.