This report was based on our clinical results of 7 patients who were treated with Kotz knee arthoplasty from 1990 to 1998. Primary bone tumors were 5 osteosarcomas, 1 malignant fibrous histiocytoma, and 1 giant cell tumor. The average age at the time of operation was 22 years (11∼47) and the average duration of follow-up was 43 months. The clinical results were estimated by ISOLS system. Rizolli X-ray method was applied to evaluate the condition of the stem. At the latest review, the average of ISOLS score was 24 (80%). On X-rays, 4 cases were classified as stage A. The other 3 cases were calssified as stage B, C, and D respectively. The X-ray of the case scored as stage D was taken only 6 months after the operation. All patients were able to walk without any assistance. These results were satisfactory.