Objectives: Although there are numerous reports comparing saphenous vein (SV) and polytetrafluoroethylene (PTFE) with respect to the patency rates for femoropopliteal bypass grafts, the clinical consequences of failed grafts are not as well described. This study compares the outcomes of failed SV and PTFE grafts with a specific emphasis on the degree of acute limb ischemia caused by graft occlusion. Methods: Over a 6-year period, 718 infrainguinal revascularization procedures were performed, of which 189 were femoropopliteal bypass grafts (SV, 108; PTFE, 81). Society for Vascular Surgery/International Society for Cardiovascular Surgery (SVS/ISCVS) standardized runoff scores were calculated from preoperative arteriograms. Clinical categories of acute limb ischemia resulting from graft occlusion were graded according to SVS/ISCVS standards (I, viable; II, threatened; III, irreversible). Primary graft patency and limb salvage rates at 48 months were calculated according to the Kaplan-Meier method. Results: Patients were well matched for age, sex, and comorbidities. Chronic critical ischemia was the operative indication in most cases (SV, 82%; PTFE, 80%; P = .85). Runoff scores and preoperative ankle-brachial index measurements were similar for the two groups (SV, 6.0 ± 2.5 [SD] and 0.51 ± 0.29; PTFE, 5.3 ± 2.8 and 0.45 ± 0.20; P = .06 and P = .12). The distal anastomosis was made below the knee in 60% of SV grafts and 16% of PTFE grafts (P < .001). Grade II ischemia was more likely to occur after occlusion of PTFE grafts (78%) than after occlusion of SV grafts (21%; P = .001). Emergency revascularization after graft occlusion was required for 28% of PTFE failures but only 3% of SV graft failures (P < .001). Primary graft patency at 48 months was 58% for SV grafts and 32% for PTFE grafts (P = .008). Limb salvage was achieved in 81% of SV grafts but only 56% of PTFE grafts (P = .019). Conclusions: Patients undergoing femoropopliteal bypass grafting with PTFE are at greater risk of ischemic complications from graft occlusion and more frequently require emergency limb revascularization as a result of graft occlusion than patients receiving SV grafts. Graft patency and limb salvage are superior with SV in comparison with PTFE in patients undergoing femoropopliteal bypass grafting.