We reviewed the radiographs of 137 patients (137 hips) who had been managed with a total hip arthroplasty, with insertion of an extensively porous-coated femoral component without cement, because of osteoarthrosis or avascular necrosis. A porous-coated acetabular component had been inserted with cement in sixty-three of these patients (Group A) and without cement in seventy-four patients (Group B). The radiographs were examined for osteolysis, either directly adjacent to the joint or at locations remote from the joint. The mean duration of follow-up was 105 months (range, fifty-four to 142 months). The rate of osteolysis of the acetabulum in the unrevised hips in which the acetabular component had been inserted with cement was 37 per cent (nineteen of fifty-one). The osteolysis was most frequently of the linear type, a pattern that was associated with a high prevalence of loosening in the hips that had a cemented cup (30 per cent [nineteen of sixty-three]). The rate of acetabular osteolysis (18 per cent [thirteen of seventy-one]) in the patients who had a cup that had not been inserted with cement and that had not been revised was not as high as that associated with the surviving cups that had been inserted with cement (p < 0.05). The osteolysis associated with the cups that had not been inserted with cement was localized and expansile, and it was not associated with loosening of the component. However, it produced more loss of bone than did the linear pattern of osteolysis around the cemented cups.(ABSTRACT TRUNCATED AT 250 WORDS)