Authors have evaluated results of the surgical treatment of congenital dysplasia of the hip joint performed at I Orthopaedic Clinic in Prague in the years 1970-1985. In the course of this period open reduction according to Ludloff was performed in seventy children out of which eight times bilaterally. Fifty-six out of the total number of seventy children same for the follow-up check. The age of the children operated on ranged between five and 23 months; in six cases the operation was performed on both hip joints. The follow-up ranged from three to eighteen years with an average of eleven years. In all children the postoperative treatment consisted in the application of the Hanausek biomechanical apparatus. On the basis of clinical and roentgenological criteria the results were divided into fair and poor results. For fair result were considered the hips with a good range of motion (none of the motions was reduced more than by 50 percent of the normal range), patients did not feel any pain, the limb shortening did not exceed 1 cm and the Trendellenburg test was negative. From the roentegonological viewpoint for fair were considered the findings without persisting subluxation and dislocation with the spheric head (the asphercity on the Moose template did not exceed 2 mm) and without evident shape deformities of the proximal end of the femur (coxa vara, overgrowth of the greater trochanter). Only such hips which meeted both the clinical and roentgenological criteria were evaluated in general as fair, the other were assessed as poor. On the basis of these criteria the result of the treatment was evaluated as fair in 76 percent and poor in 24 percent of cases. The authors also observed the incidence of aseptic necrosis of the femoral head from the viewpoint of the types defined by Bucholz and Ogden. Necrosis of Type I was not found in the group, necrosis of Type II occurred 12 times, necrosis of Type III and Type IV three times each. No evident connection was found out between the incidence of the necrosis of head and the ligation of both branches of a. circumflexa femoris medialis. The main cause of the impossibility to perform reduction was the isthmus of the joint capsula in its inferomedial portion in the area of iliofemoral ligament. Of decisive importance for the development of the joint after open reduction was a perfect reduction of the head into acetabulum.(ABSTRACT TRUNCATED AT 400 WORDS)