The etiology of congenital dislocation of the hip is still the subject of much discussion. Genetic growth disturbance, intrauterine and postnatal mechanical influences are considered as possible factors. According to Hass, typical congenital dislocation of the hip is not primarily a congenital disease. The occurance rate of C.D.H in sister or brother has been reported higher than others. But there have been no report about this cases. Two cases of C.D.H. in sister have been treated at Kang-Nam St. Mary's Hospital. Both of them were treated by traction and closed reduction under arthrography. Pavlik harness was applied in younger case after removel of hip spica cast. Clinically and radiologically the results were good during the follow-up period.