Purpose: Between 1977 and 1991,405 patients with atherosclerotic occlusive disease of the superficial femoral artery underwent clinical as well as noninvasive laboratory evaluation and were recommended for nonoperative treatment. Methods: Limbs with uncorrected aortoiliac occlusive disease, aneurysmal degeneration, or previous femoropopliteal bypass were excluded, leaving 568 involved extremities. Complete follow-up, which forms the basis for this report, was available in 377 patients (93%) with 520 limbs (93%). Patients were monitored for a minimum period of 2 years (range, 24 to 164 months; median, 86 months). During the surveillance period 45 limbs (8.6%) in 42 patients (I 1. 1%) required arterial intervention. This entailed operation in 39 cases and endovascular treatment in six cases. With use of life-table analysis, the risk for intervention was found to be 11% at 5 years and 14% at 10 years. A total of 14 limbs (2.7%) in 14 patients (3.7%) ultimately required major limb amputation, either after failed bypass (8 patients) or as a primary procedure (6 patients). Results: Analysis of risk factors revealed that female sex (p = 0.04), chronic renal failure (p = 0.0001), diabetes mellitus (p = 0.0011), history of contralateral femoropopliteal bypass (p = 0.0005), level of disease (p = 0.003), and entry ankle/brachial index less than 0.50 (p = 0.004) were associated with an increased risk over time for intervention. Other factors, including age, current or prior smoking history, hypertension, and the presence of coronary artery discase or cerebrovascular disease failed to reach statistical significance. Conclusions: These data support the continued conservative approach to surgery for patients with superficial femoral artery occlusive disease without limb-threatening symptoms. Patients with multilevel disease, lower ankle/brachial index, a history of contralateral femoropopliteal bypass, chronic kidney failure, or diabetes mellitus are at increased risk and should be monitored more closely.