The purpose was to compare radiographic parameters with a sex-matched and age-matched control group at the onset of disease and at skeletal maturity. The study comprised 143 patients with Legg-Calvé-Perthes disease, treated using a Thomas splint. Wiberg's centre-edge angle and the acetabular index angle were applied. The age at diagnosis was 6.6 years with no difference between boys and girls. At the time of diagnosis, the centre-edge angle was decreased from 18° in the control group to 10° in the affected hip. The age at follow-up was 16 (SD 2) years for the boys and 15 (SD 3) years for the girls. At the time of skeletal maturity, the centre-edge angle was decreased and the acetabular index angle increased in the affected hip and the nonaffected hip in Stulberg class III/IV/V hips compared with the control group. Initially radiographic changes only occur on the affected hip. At skeletal maturity both hips show radiographic changes.