The acetabular response to proximal femoral varus rotational osteotomy was studied radiographically in twenty-eight patients who had had thirty-three congenitally dislocated hips. All of the patients had previously been managed with open or closed reduction followed by use of a spica cast and had worn an abduction orthosis for at least one year after the reduction. The indications for the femoral osteotomy were a persistently increased acetabular index or subluxation, or both. The average age of the patients at the time of the femoral osteotomy was twenty-five months. The average preoperative acetabular index was 32 degrees. At an average of seven years after the osteotomy, the acetabular index had improved to an average of 16 degrees. Four hips had had one subsequent procedure for persistent acetabular dysplasia. Despite a failure of the acetabulum to respond to use of an abduction splint, the proximal femoral varus rotational osteotomy stimulated improvement in the acetabular index to within normal limits in twenty-nine of the thirty-three hips.