A segmental resection and rotationplasty was performed in 23 patients with malignant and aggressive benign tumor of the distal femur or proximal tibia between February 1988 and September 1992 at the Severance Hospital. There were 13 male and 10 female patients. The yongest was 5 years old and the oldest was 37 years old. Mean age at operation was 26.2 years. Of the 23 cases, 14 were osteosarcoma, 7 were giant cell tumor and 2 were synovial sarcoma. After an average observation period of 32.5 months, there was no evidence of local recurrence but 6 distant metastases were developed. According to Shriner's rating scale, the functional result were excellent or good in all cases. All patient were convinced that they had chosen the appropriate operative procedure and the ability to achieve high level of activity was considered as the main benefit.