We reviewed 39 children with cerebral palsy who had surgery for hip subluxation or dislocation. Of 55 treated hips, 31 had a varus derotation osteotomy alone, and 24 had a combination of varus derotation osteotomy and an acetabular procedure. There was no significant difference in the ages of the two groups. There was no difference in the preoperative acetabular indices of the two groups, but the average percentage of preoperative uncoverage of the femoral head was 56% in the group with varus derotation osteotomy and 63% in the group with combined varus derotation osteotomy with an acetabular procedure. The incidence of resubluxation or redislocation (24%) after varus derotation osteotomy alone was higher than that after varus derotation osteotomy with an acetabular procedure (13%). The incidence of postoperative hip instability was higher in the patients who had preoperative uncoverage of the femoral head ranging from 70 to 100%. This was in comparison with the patients who had preoperative uncoverage of the femoral head ranging from 30 to 70%. These results suggest that a combination of varus derotation osteotomy and an acetabular procedure decreases the incidence of resubluxation or redislocation, and that unstable hips with > 70% uncoverage of the femoral head should undergo the combined procedure.