Modified Van Nes rotationplasty in the treatment of malignant neoplasms in the lower extremities of children. A technique of modified Van Nes rotationplasty has been used since 1981 for limb salvage surgery in children and adolescents with malignant sarcoma of the lower extremity. The original procedure for lesions of the distal femur was further modified and adopted for selected lesions of the proximal femur and tibia. Sixteen skeletally immature children form the base of this report. The tumors were located in the distal femur in ten children, the proximal tibia in five and the proximal femur in one. There were no intraoperative complications and postoperative complications included one infection requiring debridement and three minor healing delays. There were no local recurrences, neurovascular compromises, late derotations, or psychologic decompensations. One patient died of metastatic disease and another died of a second malignancy (leukemia). The remaining patients are good, functional, below-knee prosthesis users who participate in a number of sporting and athletic activities. The procedure is safe, has a relatively low complication rate, allows for the functional demands of an active, growing child, and accommodates for the future growth of extremities. 