Between January 1973 and January 1988, 188 patients with unilateral iliac artery occlusion were treated at The Middlesex and University College Hospitals, 185 for primary disease and three for blockage of a previous aortobifemoral graft. In the early part of the series, a variety of operations, including aortofemoral and iliofemoral bypass, and endarteriectomy, was used. Femorofemoral bypass was at first reserved for patients who were considered unfit for major surgery, but the results seemed so good that it was adopted as the procedure of choice. Latterly, percutaneous transluminal angioplasty became available, and the role of this is discussed. Over the 15-year period, 150 patients underwent femorofemoral bypass (all but two receiving a prosthetic graft). Of these, 90 per cent had disabling claudication and 8 per cent had critical ischaemia. There were six early deaths (within 30 days of operation) and five late deaths, and two surviving amputees; nine patients could not be traced. The remaining 128 patients have been assessed at intervals of from 3 to 92 months, both clinically and with Doppler studies. The cumulative patency was 86 per cent at 13 years, and all of these patients experienced subjective and haemodynamic improvement in the recipient limb. Eight grafts occluded in the early postoperative phase. In five patients there was deterioration in the donor limb; it is postulated that the effect was due to causes other than the operation. There were two serious postoperative complications due to technical error, one of which led to early above-knee amputation. These are presented in detail. In the light of this experience, the advantages and indications for femorofemoral bypass and the results to be expected from it have become clarified, and the technique standardized so that errors can be avoided. We suggest that femorofemoral bypass is now the operation of choice for unilateral iliac artery occlusion.