In order to investigate the validity of the Steel's gluteus medius and minimus advancement, we reviewed 21 hips in 14 spastic cerebral palsy patients, who had advancement of the gluteus medius and minimus insertion for the correction of in-toeing gait between November 1985 and February 1992. The procedure was limited to those patients who had moderate to severe in-toeing gait with positive Steel's stretch reflex. There were eight boys and six girls. The average age at the time of surgery was 6.7 years(2.9 years-11.9 years). The procedure was performed on both hips in seven patients. Of the 14 patients, nine had diplegia, three hemiplegia, and two paraplegia. The average follow-up time was 4.3 years(1 year-8.5 years). In-toeing gait was converted to neutral or physiologic out-toeing gait in 17 hips(81%), excessive out-toeing in 2 cases(9.5%), and mild residual in-toeing in 2 cases(9.5%), Steel's stretch reflex, which was present in all cases preoperatively, disappered in 19 hips(90.5%) postoperatively, Abductor power, however, decreased from 4+ to 4− in average postoperatively, Among the 16 hips, which had no Trendelenburg sign or gait preoperatively, 8 hips(50%) showed positive Trendelenburg sign and gait postoperatively. In conclusion, Steel's gluteus medius and minimus advancement appears to be effective in the correction of in-toeing gait, but there is high risk of weakening the abductor power.