Giant cell tumor is an uncommon primary bone tumor of young adults with the highest incidence in patients 20 to 40 years of age. These tumors are most frequently found in the metaphyseal-epiphyseal region of the long bones, especially around the knee joint and the distal end of the radius. So the normal life expectancy and an active life style of the patient necessitate a reliable and durable surgical remedy for eradicating the tumor and preserving joint function. Furthermore, these have an unpredictable clinical behavior. Although almost always benign, these tumors are locally agressive and tend to have a high rate of rerurrence, and malignant transfomation is well known to be 6 15%. Thus the lesions produce a practically difficult therapeutic problem for the orthopaedic surgeon, and a satisfactory method of treatment has not yet been found. Clinical observations were carried out on 33 cases of giant cell tumor of bone in the Department of Orthopaedic Surgery, Yonsei University College of Medicine from May 1975 through May 1985, and the following results were obtained. 1. The highest incidence, 23 cases (70%), accurred in the 21 40 year old age group, and the sex distribution was 18 males and 15 females. 2. The most frequent locations were the distal feuiur, proximal tibia and distal radius. Twenty four cases(73%) occurred around the knee joint. 3. The pathologic grading according to Jaffes criteria showed 10 cases(30.3%) in grade I, 20 cases (60.6%) in grade II and 3 cases(9.1%) in grade III. 4. As the primary treatment modality, currettage and bone graft were performed in 9 cases, currettage and bone cementing in 9 cases, amputation or disarticulation in 7 cases, enbloc excision with or without other procedures in 6 cases and currettage and radiotherpy in 2 cases. 5. Eight cases(24.2%) recurred after primary treatment and 6 cases of the 8 recurrences appeared within 2 years after primary treatment. 6. Four of the 9 tumors treated by currettage and bone graft recurred, as did two of the 9 tumors treated by currettage and bone cementing. No recurrence occurred in the 7 tumors treated by amputation or disarticulation. 7. As the secondary treatment modality for 8 recurrences, amputation or disarticulation was performed in 5 cases.