1. Forty-one giant-cell tumors of bone observed at the Massachusetts General Hospital between 1925 and 1960 have been presented. There were thirty-one Grade I and ten Grade II tumors.

2. Eleven of the patients were under twenty years of age.

3. The over-all recurrence rate for Grade I tumors was 48 per cent and for Grade II tumors, 70 per cent.

4. On the basis of this study we recommend total excision, if surgically feasible, as the treatment of choice. When total excision is not feasible, curettage is advised with an expected recurrence in more than half of the patients. Radiation alone or combined with curettage or partial excision produced remarkably inferior results in this series.

5. Four of the forty-one tumors underwent fibrosarcomatous transformation, two of ten Grade II tumors and two of thirty-one Grade I tumors. Thus, the incidence of malignant degeneration was three times higher in the Grade II tumors. There was little evidence to suggest definite relationship between irradiation and malignant transformation. Sarcoma developed in only two of the sixteen patients receiving radiation treatment. However, the follow-up on several of these patients is relatively short.

6. Six of the forty-one patients had sacral tumors. These tumors had a poor prognosis and a higher incidence of malignant transformation than lesions in other locations.