From October 1977 to October 1982, 363 unilateral aorto-femoral bypasses using polytetrafluoroethylene (PTFE) prostheses were performed for predominantly unilateral aorto-iliac disease. The distal anastomosis was extended into the deep femoral-artery in 57% of the patients. The postoperative mortality was 0.5%. The actuarial patency rate after 6 years was 87% in patients with claudication and 77% in those with critical ischemia. No false aneurysm developed. Thrombosis of the prosthesis was due to progression of distal disease, intimal hyperplasia and postural extrinsic compression. The latter seems to be characteristic of PTFE prostheses and can be treated by thrombectomy. In 21 cases a cross-over femoro-femoral bypass was done during the follow-up period because of contralateral progression of disease.