One hundred thirty-seven developmentally dysplastic hips of 107 children with a mean age of I I months were treated by the same surgical algorithm. Following iliopsoas and adductor longus tenotomies by the Ferguson posteromedial approach, the operation was ended in case of arthrographically documented concentric reduction (Tonnis grade I reduction) and an open reduction was performed in case of nonanatomic arthrographic reduction (Tonnis grade 2 or 3 reduction). Mean follow-up was 4.2 years. The need for open reduction increased in preoperatively dislocated hips that were proximally displaced according to the Tonnis classification. Somewhat better latest acetabular index values were seen in hips having lower preoperative dislocation grades that were surgically treated before the age of 12 months. Rates of avascular necrosis of the femoral head, redislocation, and secondary operation were 13%, 1%, and 2%, respectively. The authors concluded that although mid-term results of this new surgical algorithm in developmental dysplasia of the hip was satisfactory in infants younger than 18 months of age, long-term follow-up is needed for better understanding of its use.