76 consecutive Charnley low friction hip arthroplasties were performed in 54 (37 men) patients with ankylosing spondylitis from 1971 to 1991 in the Rheumatism Foundation Hospital. Their mean age was 40 (16-67) years. They were followed until the end of 1999. The overall prosthesis survival was 80% at 10 years, 66% at 15 years and 62% at 20 years. The survival of the acetabular component was 91%, 77% and 73% at 10, 15 and 20 years and that of the femoral component 82%, 79% and 77%, respectively. We found no significant risk factor that predicted prosthesis survival.