Of 327 patients who had a giant-cell tumor of bone and were seen at the Istituto Rizzoli, 293 were treated at the Institute, and 280 of these were followed for two to forty-four years. The distribution according to sex and age of the patient and site of the tumor was similar to the distributions in major reports of large series. The tumor usually involved the metaphysis and the epiphysis, but was occasionally limited to the metaphysis, and in only 2 per cent of the patients was it adjacent to an open growth plate. The tumor on occasion invaded the articular space, also involving the ligaments and the synovial membrane. Extension to an adjacent bone through the joint occurred in 5 per cent of the tumors. Our radiographic grading, which is roughly comparable with the staging system of Enneking et al., was Grade I in 4 per cent, II in 74 per cent, and III in 22 per cent of 266 patients before treatment. A pathological fracture was apparent on the first radiograph in 9 per cent of the patients. In the 280 patients with adequate follow-up, 331 surgical procedures were performed. The rate of local recurrence was 27 per cent in the 151 intralesional procedures, 8 per cent in the 122 marginal excisions, and zero in the fifty-eight wide or radical procedures. These results did not correlate with the radiographic grade of the lesion. Of the fifty-one local recurrences that were seen after treatment at our institution, 90 per cent appeared in the first three years after surgery.(ABSTRACT TRUNCATED AT 250 WORDS)