The results in 114 hips of ninety-two patients who had osteonecrosis of the femoral head were assessed after treatment with core decompression. The average duration of follow-up was three years and four months (range, two years to six years and six months). The average age of the patients was forty-one years (range, fifteen to sixty-seven years). The presumed risk factors were the use of corticosteroids (thirty-seven hips), excessive use of alcohol (thirty-two hips), trauma (seven hips), and various other factors (seven hips). No specific risk factor was identified for thirty-one hips, and the osteonecrosis was considered to be idiopathic. The preoperative evaluation consisted of clinical assessment, magnetic resonance imaging, and radiographic staging according to a modification of the system of Ficat. Thirty-two hips were in stage I; thirty-eight, in stage IIA; twenty-five, in stage IIB (transition stage, with a crescent sign); and nineteen, in stage III. Clinical failure was defined as the performance of a subsequent operation. Over-all, sixty-four hips (56 percent) failed clinically. Fifty-seven were treated with a hip replacement; four, with a femoral osteotomy; and three, with a vascularized fibular graft. Clinical failure was seen in five (16 percent) of the thirty-two hips in stage I, twenty (53 percent) of the thirty-eight hips in stage IIA, twenty (80 percent) of the twenty-five hips in stage IIB, and in all nineteen of the hips in stage III.(ABSTRACT TRUNCATED AT 250 WORDS)