We reviewed 23 patients with a giant-cell tumour (GCT) of bone and histologically-proven lung metastases at a mean of 11.9 years (3 to 24.5) after the original diagnosis. The mean age of the patients at diagnosis was 27.3 years (9 to 61); the male to female ratio was 0.9:1. The most common primary site was the distal radius. The mean interval between the onset of the tumour and the detection of lung metastases was 4.1 years (0 to 24). There had been local recurrence in 19 (83%) either before or at the time of diagnosis of lung metastasis. Surgical resection alone was the preferred treatment for lung metastases in 70% and resulted in 18 patients (76%) being free from disease when last reviewed. One patient had the spontaneous regression of lung metastases and was free from recurrence 16 years later. Sixteen patients (69.7%) have survived and four (17.4%) have died from progression of the tumour. Three other deaths were not related to the tumour. Local recurrence and a primary lesion at the distal radius seem to be associated with an increased risk of lung metastases. Repeated surgical resection of lung metastases gave a high rate of survival.