This study compared the clinical and radiographic results and the prevalence of osteolysis between alumina-on-alumina and alumina-on-highly cross-linked polyethylene bearings after cementless total hip arthroplasties in the 100 patients younger than 50 years of age. There were 66 men and 34 women; the mean age at the time of surgery was 45.3 years (range, 25 to 49 years). The mean duration of follow-up was 5.6 years (range, five to seven years). The pre-and postoperative Harris hip scores were similar (39 and 41 points, respectively and 93 points and 94 points, respectively). No acetabular or femoral component had aseptic loosening in either group. The mean annual penetration of the highly cross-linked polyethylene was 0.06 +/- 0.03 mm. No hip in either group had acetabular or femoral osteolysis.