In cases of developmental dysplasia of the hip (DDH) where reduction of dislocation was difficult to achieve with conservative treatment, open reduction (OR) using the extensive anterolateral approach has been applied at our facility since 1992. - The post-operative course following OR was investigated at our facility and the factors responsible for a poor outcome were analyzed. The study involved 22 patients (24 operated hips) who were followed for 14 years or more after OR had been performed at age 3 or less at our department or in affiliated hospitals. Using plain X-ray, the preoperative α angle as well as CE angle and Sharp angle during the last visit were measured, accompanied by evaluation using Severin classification, evaluation of femoral head necrosis according to Kalamchi and MacEwen classification and evaluation of arthritic changes. At the last visit, 17 hips (70%) were rated as Severin group I or II. There were 3 hips (12.5%) rated as Kalamchi and MacEwen group II, III or IV and all 3 were affected by femoral head necrosis. Arthritic changes were seen in 3 hips (12.5%). Corrective surgery had been additionally performed on 4 hips. The results suggest that two preoperative factors, early diagnosis and conservative treatment method, and an intraoperative factor, surgical stress on the hip, are associated with a better long-term outcome after surgery using the wide exposure technique. Furthermore, since some cases showed improvement of the hip joint acetabular cover during the follow-up period, corrective surgery for preschool-- aged children should be carefully considered.