With use of porous-coated implants, total hip arthroplasty was performed in a consecutive series of thirty patients (thirty-five hips) who had a preoperative diagnosis of late-stage (Ficat and Arlet stage-III or IV) osteonecrosis of the femoral head. The patients were evaluated clinically and radiographically, and the data were recorded in a prospective manner. The average duration of follow-up was seven and one-half years (range, five to ten years). The average age of the patients at the time of the operation was thirty-two years (range, twenty-one to forty years). Signs of osseointegration of the femoral stem to the host bone were demonstrated in thirty-three hips (94 per cent). In the porous-coated hemispherical acetabular cups of these hips, an optimum bone-implant interface was identified and maintained, suggesting bone ingrowth. The rate of revision was 3 per cent (one hip) for the femoral side and 6 per cent (two hips) for the acetabular side, for an over-all rate of 6 per cent. All patients maintained a high level of activity postoperatively. There was moderate or severe remodeling of proximal femoral resorptive bone and stress-shielding in six hips (17 per cent) and osteolytic reactions in six hips. Complications were frequent (six hips) and included one deep infection; two dislocations; two instances of heterotopic ossification; and one fracture of the calcar femorale, which occurred intraoperatively. The thirty patients had a lower rate of revision and improved clinical outcomes compared with other reported series of young patients managed with total hip arthroplasty with cement who had the same diagnosis and similar postoperative follow-up. However, the latter series involved implants of an earlier design that had been inserted with older techniques of cementing. When arthroplasty is considered for the treatment of late-stage osteonecrosis of the femoral head in young patients, the use of total hip implants without cement that allow for bone ingrowth appears to be a viable alternative to arthroplasty with use of cement. However, longer follow-up is needed to determine the outcome of the osteolytic reactions that we observed. We therefore recommend this procedure with some caution because of the high rate of complications and the potential for failure of the arthroplasty related to the osteolytic reactions.