Multifocal occurrence of peripheral atherosclerotic aneurysm is well known. However, little attention has been directed to subsequent progressive aneurysmal development adjacent to sites of previously resected and grafted popliteal aneurysms. During a 20 year follow-up study of 79 patients with 115 popliteal aneurysms, we have observed the development of six atherosclerotic femoropopliteal aneurysms adjacent to the original aneurysm site in four patients, occurring 5 months to 10 years (average, 5 1/2 years) after the initial operation. Operative repaire was accomplished successfully of five of the six aneurysms; one popliteal aneurysm has not been operlateral popliteal aneurysm (46 percent). Fifty-seven patients (72 percent) presented with complications of the aneurysm, including 35 with thrombosis. As initial therapy, 69 grafting procedures were performed on 58 patients; nine extremities had sympathectomy only; four aneurysms were ligated or resected without grafting; and four extremities required amputation as the only procedure. Among patients with grafts, nine subsequent amputations were necessary in the early postoperative period, all occurring in patients presenting with thrombosed aneurysms. No patient who developed pedal pulses in the period immediately after operation required amputation. In addition, two patients developed aneurysmal degeneration in popliteal homografts. These data demonstrate the progressive nature of popliteal aneurysmal disease and emphasize the need for regular and life-long follow-up.