Thirteen patients who had a proximal femoral focal deficiency and were treated with a rotational osteotomy of the tibia (Van Nes procedure) were evaluated at an average of five years after operation. Five patients needed a repeat osteotomy of the tibia: four because the limb had spontaneously derotated toward the original position and one because the limb had had insufficient rotation at the time of operation. One patient had a disarticulation at the ankle after the first stage of a planned two-stage procedure because the mother was not happy with the child's appearance. In ten limbs, the distal femoral growth plate and epiphysis were removed and in two, the femoral epiphysis and growth plate and the tibial growth plate were removed so that the joint of the prosthetic knee would be positioned at the proper height at the completion of the child's growth. Neither growth plate was removed from one limb, the shorter one in the child who had bilateral involvement. A ten-point grading scale based on use and fit of the prosthesis, gait, range of motion of the ankle, use of external support, and final height of the ankle compared with that of the contralateral knee was used to evaluate the result, which was excellent in six patients, good in four, fair in one, and poor in one. One patient, who had a disarticulation at the ankle, was excluded from the final evaluation. Rotational osteotomy provided good function and acceptable cosmetic appearance in the patients who had unilateral involvement.