Giant cell tumor is rather uncommon tumor of cancellus bone usually considered benign but with malignant degeneration in about 10 % cases. It is apparent form the literature that the pathologic diagnosis of giant cell tumor may be difficult and that correlation with roentgen and clinical finding is essential in most cases. Authors present 23 cases of giant cell tumor, confirmed at Seoul National University Hospotal form 1971 to 1980 and analyze their clinical and radiological findings. The result are follows : 1. The 3 rd-4th decade is the predilection age and female exceeds male in ratio of 1.9 : 1. Presenting symptoms are pain, painful swelling, selling and stiffness in order of requency. 2. The favorite locations are the distal end of fumur , proximal end of tibia and proximal end of femur in order of frequency. 3. The lesion is eccentric in most of the cases with variable form in transitional zone-sharp, permeative and fade out pattern. Decreased homogenous radiolucency a d trabeculation are showed in same ratio. Among the 17 cases(73.9%) of expansile lesion, 12 cases (70. 6%) . Soft tissue swelling is seen in 6 cases(21.6%), and pathologic fracture 5 case (21.7%).