We studied the results of surgical treatment for rotational deformities of the lower extremity in fifty children. The preoperative rotational deformities were subdivided as follows: (1) external rotation deformity of the hip (nine hips), (2) external tibial torsion (twenty-nine limbs), and (3) toeing-in gait (thirty-one limbs). These were further analyzed as to imbalance between the forces of the medial and lateral hamstrings, that imbalance associated with fixed internal tibial torsion, and isolated internal tibial torsion. The average length of follow-up was four years and six months. For the external rotation deformity of the hip we performed a derotation osteotomy with internal fixation at the subtrochanteric level. That procedure led to eight good results and one fair result. The external tibial torsion was treated by a derotation osteotomy of the tibia and fibula distally, with correction of the valgus deformity of the ankle if that was more than 10 degrees. In twenty patients a good result was obtained. For the toeing-in gait associated with a medial-lateral hamstring imbalance, the semitendinosus was transferred to the biceps and the head of the fibula. Good results were seen in ten of the fourteen patients. In twelve limbs a derotation osteotomy of the distal ends of the tibia and fibula was done alone, with eight good and fair results. In five patients a simultaneous semitendinosus transfer and derotation osteotomy was used. All had a good result. The over-all rate of good and fair results in the entire series was 79.6 per cent.