Data on 240 primary Charnley total hip arthroplasties, performed in 211 patients from October 1968 to July 1974, were recorded prospectively. Fifty-two prostheses were implanted in forty-six patients who were thirty-four to fifty-five years old, and 188 prostheses were implanted in 165 patients who were more than fifty-five years old. The results for the younger patients were compared with those for the older patients. Twenty hips were revised over-all, and all five of the infections and four of the five fractures of the femoral stem that occurred in this group were in the older patients. However, the rate of aseptic loosening was similar for the two age-groups (three of the hips in the younger patients and five in the older patients). The probability of revision after twenty years for the two groups, as determined with Kaplan-Meier analysis, was 11.7 per cent for the younger patients and 10.7 per cent for the older patients. There was no significant difference between the two groups with regard to either the number of revisions or the percentage of patients who had radiographic signs of loosening. The median Charnley hip scores during the course of the study were also similar for the two groups. We recommend that Charnley low-friction arthroplasty be used even in younger patients, as the long-term results were excellent and were comparable with those in the elderly age-group.