Attention to the radiographic shadow of the walls of the acetabulum seen on the anteroposterior projection of a well-centered radiograph of the pelvis is important to identify the orientation of the opening of the acetabulum. This is referred to as the acetabular version. The opening of the mouth of the acetabulum may be oriented anteriorly, which is referred to as anteverted; posteriorly, or retroverted; or when the shadow of the lips of the anterior and posterior walls terminate together on the lateral edge of the acetabular rim, neutral version. The radiographs of 153 patients with developmental hip dysplasia presenting with hip pain were reviewed to determine the frequency of retroversion of the acetabulum. In this group of patients, retroversion of the hip socket was surprisingly common, one in three hip sockets, and generally was associated with smaller values of the lateral center edge measurement. The observation is important, because it must be taken into account when planning a corrective osteotomy of the acetabulum so the abnormal horizontal orientation of socket is corrected along with the usual anterior and lateral insufficiency.