This study aimed to evaluate the outcome of medial open reduction for developmental dysplasia of the hip (DDH) in patients before and after walking age. A minimum 5-year radiographic and clinical follow-up compared 29 patients (group 1) before walking age with 38 patients (group 2) after walking age for DDH. The correction ratio of acetabular index was similar in both groups postoperatively (41.8% for group 1 and 44.9% for group 2), and it was statistically not significant (P>0.05). The Kalamchi-MacEwen classification showed no correlation between operative age and the rate of avascular necrosis (P>0.05). This report presents similar complication rates as that of the Severin criteria for medial open reduction of the hip and challenges the conventional belief that a medial open reduction for the treatment of DDH in a walking-age child at short-term to mid-term follow-up has comparable results.