The results of rotationplasty for patients with osteosarcoma around the knee joint are presented. After an average observation period of 13.3 months, there has been no local recurrence or metastasis. The ankle joints (the new knee joints) of the patients were able to support their body weight with an average range of motion of 75 degrees. All patients could walk well without crutches and without risk of the giving way phenomenon. The average rate of the functional evaluation according to the re-modified system by Enneking was 84.5% (range, 80.0-86.7%). No patient had psychological trouble in accepting the shortened and rotated extremity. The results show that rotationplasty is a useful reconstructive method for the treatment of osteosarcoma around the knee joint.