The authors made a review of twenty cases of congenital dislocations of the hip which had been of unilateral involvement and followed up for more than 3 years after reduction regarding differences and changes of the acetabular floor thickness, femoral head diameter and long leverage. l. Acetabular floor thickness at initial diagnosis was 7.3mm in normal and 9.6mm in dislocated side on average. 2. At 3 years follow up, the acetabular floor thickness was found as increased by 3.1mm in average in normal side and 4.2mm in affected side, The hips reduced before 1.5 years of age showed only 0.6mm increased in average, and those reduced after 1.5 years showed 1.5mm increment compared to normal side at 3 years followup. 3. The femur head diameter at 3 years follow up were 25.8mm in normal side, 27.4mm in disloacated and the distance of the femur head center from that of body were 62.2mm and 68.Omm, respectively, more distinctly displaced in dislocated side. The authors noticed that the increments of the above three measurements were marked in the affected side than the uninvolved side and it seemed less remarkable in cases which were reduced early, especially before the age of 1.5 years.