Giant cell tumor is rather uncommon tumor of cancellous bone usually considered benign but with malignantdegeneration in about 10% of cases. It is apparent from the literature that the pathologic diagnosis of giant celltumor maybe difficult and that correlation with roentgen and clinical finding is essential in most cases. Authorspresent 23 cases of giant cell tumor, confirmed at Seoul National University Hospital from 1971 to 1980 andanalyze their clinical and radiological findings. The results are as follows; 1. The 3rd-4th decade is thepredilection age and female exceeds male in ratio of 1.9:1. 2. The favorite locations are the distal end of femur,proximal end of tibia and proximal end of femur in order of frequency. 3. The lesion is eccentric in most of thecases with variable form in transitional zone-sharp, permeative and fade out pattern. Decreased homogenousradiolucency and trabeculation are showed in same ratio. Among the 17 cases (73.9%) of expandile lesion, 12 cases(70.6%) reveal cortical erosion. Soft tissue swelling is seen in 6 cases (26.1%) and pathologic fracture 5 case(21.7%),