In this study, we aimed to evaluate the long-term clinical and radiological results of single-stage open reduction through a medial approach and Pemberton acetabuloplasty in developmental dysplasia of the hip. We treated 32 hips (22 patients) with developmental dysplasia by a single-stage open reduction through Ferguson’s medial approach and Pemberton acetabuloplasty. The procedure was performed bilaterally in 10 patients. The mean age of the patients at the time of the operation was 19.8 months (16–24 months). The mean follow-up period was 10.9 years (7–19 years). Group I avascular necrosis according to the Kalamchi and MacEwen classification was observed in two hips and group II in one hip. Radiologically, 90.6% of the hips were classified as Severin class I and 9.4% of the hips were classified as Severin class II. At the latest follow-up, 30 hips were assessed clinically as excellent and two hips as good. No patient required subsequent surgery. We conclude that single-stage medial open reduction and Pemberton acetabuloplasty represent an effective method for developmental dysplasia of the hip in children older than 15 months of age.