Prospective, randomized comparison of ringed and nonringed polytetrafluoroethylene femoropopliteal bypass grafts: a preliminary report. Kinking and compression with knee flexion are thought to be one cause of failure of below-knee polytetrafluoroethylene femoropopliteal bypass. To prevent this problem polytetrafluoroethylene grafts externally supported with rigid rings have been developed. The present randomized, prospective study compared ringed and nonringed polytetrafluoroethylene grafts in 122 patients who underwent femoropopliteal bypass for severe limb ischemia. Patients were well matched for surgical indications and risk factors. There was no significant difference in the 3-year graft patency rate of ringed versus nonringed polytetrafluoroethylene femoropopliteal bypasses (74% vs 68%, p = 0.5). Similarly, no significant differences were found in the 3-year graft patency rates of ringed versus non-ringed above-knee (82% vs 74%, p = 0.5) or below-knee polytetrafluoroethylene femoropopliteal bypasses (68% vs 59%, p = 0.5). The 3-year graft patency rate of all above-knee polytetrafluoroethylene femoropopliteal bypasses was slightly greater than that of below-knee polytetrafluoroethylene femoropopliteal bypasses (76% vs 62%), but this difference was not statistically significant (p = 0.25). The 3-year limb salvage rate with ringed polytetrafluoroethylene grafts was 92% compared with 79% for nonringed polytetrafluoroethylene grafts, but this difference was not statistically significant (p = 0.25). Data to date from this study fail to support the recommendation that ringed polytetrafluoroethylene grafts be used preferentially over conventional polytetrafluoroethylene grafts in patients who require femoropopliteal bypass with a synthetic graft. 