The objective of this prospective, controlled study was to assess the radiographic course of acetabular develop- ment in developmental dysplasia of the hip (DDH). The study consisted of 14 patients (mean age at operation, 12 months; range, 6 to 18 months) from a large, prospective series diagnosed with unilateral DDH and treated by a soft tissue surgical procedure via the posteromedial approach. All patients had intraoperative radiographic anatomic reductions, did not have any type of complica- tion during follow-up, and were followed until at least 10 years of age. Unaffected contralateral hips were used as controls. The acetabular angle of Sharp (AA) was measured to determine acetabular development. Mean follow-up was 112 months. A significant difference (p < 0.005) was observed between the mean AA values of affected and unaffected hips at operation and at the first three follow-up visits (mean age was 24, 41, and 56 months, respectively). This significant difference was not present (p > 0.05) at the latest two follow-up visits (mean age was 90 and 124 months, respectively). It can be concluded that a marked radiographic improvement in acetabular slope occurs within 1 year postoperatively. This improvement continues slowly during the childhood period, and the acetabulum attains previously determined normal AA values at nearly 7 to 8 years of age for those patients whose dysplastic hips were anatomically reduced at less than 18 months of age and for those who did not experience complications during follow-up.