It is well-known that early diagnosis and treatment is still the most important aspect of congenital dislocation of the hip. However, the orthopaedist can not see the cbildren with dislocated hip before they begin to Walk, especially in the developing countries. When the children with dislocated hips are discovered lately,it is impossible to reduce the hip by simple manipulation, and also is very difficult to maintain the reduction successfully. Our method of treatment was based on the concept that the various components of the abnormal joint will develop satisfactorily into a normal hip provided acccurate congrucus and concentric reduction is obtained as early as possible to take advantage of the maximum growth potential, and is maintained throughout growth, In this study 16 children with 18 dislocated hips among the 75 children with congenitally dislocated hips were primarily treated by open reduction,followed by 3 weeks of temporary fixation of reduced hip by Kirschner wire and 6 weeks of cast immobilization from November 1973 to April 1979. They were clinically and roentgenologically analized. The end results of treatment were assessed by 3 roent- genological determinants; the medial joint space, the acetabular angle and the centeredge angle. The results obtained were as follows: 1. The pathologically widened medial joint space of hip or hips decreased rapidly during first 6 months after reduction, irrespective of the age at reduction, and satisfactory results were obtained in 83 per cent indicated by joint space distance less than 10 mm. 2. Postoperative Kirschner wire fixation of reduced hip to maintain the reduced position did not impair the physeal growth or bring the joint stiffness. 3. The acetabular angle improved rapidly during the first year after reduction in all age groups of patients and thereafter the rate of acetabular development decreased, but the acetabular angle continued to improve throughout the period of observation and satisfactorily (less than 25 degrees) developed in 83 per cent of children. 4. The center-edge angle increased rapidly during first three months after reduction and was satisfactory (more than 20 degrees) in 78 per cent. Overall success rate of treatment was 81.3 per cent. 5. Assessment of end results by medial joint space has more advantages in evaluating the result of treatment because of the aimplicity of it's measurement and leas error regardless of the change of patients position on roentgenagrams. 6. There were only few complications (11.1%) after surgical treatment; coxa magna in a case and resubluxation in another case were complicated. 7. Parameters utilized for assessing the results were faund to be the very helpful criteria to evaluate the hip development indicated by cephalocotyloid relation when used together. 8. Simultaneous open reduction followed by temporary internal fixation with K-wire was found to be recommendable method of treatment ae a first choice of treatment even in children under age of 3 if once nonsurgical reduction fails; because by this type of treatment more easily and accurately concentric reductions were obtained, and also reduction was more easily maintained without subsequeat redislocation.