After resection of a malignant bone tumor of the femur, rotationplasty is considered a treatment option in addition to other limb salvage procedures such as endoprosthetic replacement, allograft, or autograft reconstruction. A Type B IIIa rotationplasty is indicated when the tumor involves the total femur or when skip lesions are detected. After the total femur is resected, the lateral tibial plateau is placed into the acetabulum after rotating the tibia and foot segment 180 degrees. Eight patients at an average age of 5.9 years underwent a rotationplasty Type B IIIa at the authors' institution. After a median followup of 59.6 months (range, 24-86 months) the clinical results were excellent and the functional status according to the criteria of the Musculoskeletal Tumor Society was good (23 of 30 points). In electromyographic analysis the muscle activity of the affected leg revealed good function of the stance and the swing phase muscles according to their new function with comparable amplitudes to the unaffected limb. The kinematics (range of motion of the hip and knee) were slightly assymmetric. Gait analysis showed a slight lateral trunk lean over the ipsilateral limb with reduced joint moment. All patients had full weightbearing ability. Remodeling of the tibial plateau into a round form mimicking a new femoral head is confirmed by radiographs and magnetic resonance imaging scans. In young children with a tumor of the total femur, rotationplasty Type B IIIa is a good treatment modality with excellent clinical and good functional results. The electromyographic and gait analysis data underscore a good functional restoration of gait after rotationplasty.