Changes in the acetabulum play an important role in the final results of Legg-Calvé-Perthes disease (LCPD). To determine the relationship between the acetabulum and the final results, the acetabulum was measured in 108 children with unilateral LCPD. The acetabular radius, depth, width; iliac width and height; and medial joint distance were measured on the radiographs initially and on follow-up. The parameters between the affected and the unaffected sides were compared by using t test. Herring's classification was employed to evaluate the extent of involved femoral head. The results showed that the radius of the acetabulum was the most sensitive measurement representing the pathologic changes in the acetabulum. The acetabular hypertrophy occurred very early in the avascular necrosis stage. It resulted in the lateral subluxation of the femoral head and in loss of containment. During the later stage of the disease, the femoral head overgrew and broke the growth limit of the acetabulum. Coxa magna made it difficult for a hypertrophic acetabulum to contain it.