A segmental resection of the distal femur and proximal tibia including the knee joint and rotationplasty was performed in 8 patients with malignant and aggressive benign tumor of the distal femur or proximal tibia between January 1988 and October 1989 at the Severance Hospital. There were 5 male and 3 female patients. The youngest was 17 years old and the oldest was 37 years old. Mean age at operation was 26.2 years. Of the 8 cases 3 were osteosarcoma, 3 were giant cell tumor and 2 were recurrent giant cell tumor. Among the 3 patients with osteosarcoma, 1 patient had undergone preoperative and postoperative chemotherapy and 2 patients had undergone postoperative chemotherapy only. Of the 8 patients, 1 patient developed local cutaneous necrosis and in 2 cases, pseudarthrosis between the tibia and femur developed. Both cases underwent revisional surgery with resulted in stable osteosynthesis. Early fitting of the prosthesis and ambulation were possible in all cases. After an average observation period of 18.5 months (range 13 months to 30 months) there was no evidence of local recurrence and detectable distant metastasis. Because of the success in preventing local recurrence and excellent functional results in these 8 patients, we now recommend this method in surgical management of malignant and benign aggressive tumors of the distal femur and proximal tibia in young people.