Forty-four developmentally dislocated hips occurring in 30 patients with an average age at initial surgery of 10.7 (range 2-19) months underwent medial open reduction by Ferguson's approach. All patients were skeletally mature at most recent evaluation. Mean follow-up was 19.8 (range 13-27.5) years. No redislocation or sub-luxation occurred. Additional surgery was required in 11 hips (25%). Avascular necrosis was detected in nine hips (20%). The acetabular index was decreased and the center-edge angle was increased during follow-up. Excellent or good outcome (Severin group 1 or 2) was observed in 79% of the hips at skeletal maturity. At the most recent evaluation, all but two patients had the highest score on the Iowa Hip Rating. The authors conclude that open reduction through the medial approach is effective in developmental dislocation of the hip. Follow-up until skeletal maturity is necessary for an accurate assessment of treatment.