Forty-seven cases of giant cell tumor of bone were clinicopathologically reviewed to determine any useful prognostic factors. Disease recurred in 11 cases. Eight of these cases had initially been treated with intracapsular piecemeal excision and three cases had been treated with wide excision. Nine of the 11 cases were classified as Grade III, two cases as Grade II, and one case as Grade II + fracture according to Campanacci's radiographic grading system. Intracapsularly excised cases had a high recurrence rate (47.1%). Metastasis to the lung occurred in three cases, each of which had been classified as Grade III. Although the radiographic Grade did not correlate with the rate of lung metastasis or recurrence, cases that metastasized to the lung or recurred tended to be radiographically aggressive. Disease recurred in eight of 24 Grade III cases; but in only two of 12 Grade II cases, in one of five Grade II + fracture cases, and none of six Grade I cases. p53 was expressed by mononuclear stromal cells in six cases. Disease recurred in four and lung metastasis occurred in three of these cases. p53 Expression correlated with rates of lung metastasis and recurrence. It was concluded that cases in which p53 is expressed have a high potential for lung metastasis and recurrence.