Objective To observe the clinical features of the femoral head necrosis caused by a gross teres ligament after reduction of developmental dislocation of the hip and study its pathological causes.Methods Ten hips with necrosis of the femoral head after reduction of developmental dislocation of the hip were observed. X-ray images of the hip were retrospectively reviewed with regard to the acetabular index, the acetabular-head index, the shapes and the development of the femoral heads. The operative findings were analyzed.Results No growth or delayed growth of the femoral head and the acetabular index was found after reduction. The recovery of acetabulum was very slow. All of the cases showed the same features: femoral head necrosis, subluxation, and acetabular dysplasia. A gross teres ligament was proved during surgical operation. The femoral head recovered gradually after the operation.Conclusions The gross tissue interposed (a gross teres ligament) is another important pathogenesis of femoral head necrosis after the reduction of developmental dislocation of the hip. It is necessary to recognize it before reduction by imaging examinations.