Angiography was performed on 48 patients with giant-cell bone tumors. Sixty-four per cent were hypervascular; 25% were hypo- or moderately vascular; and 10% were avascular. Findings were similar in the 45 benign and 3 malignant tumors. There was no correlation between the findings and degree of histological aggressiveness. There was a high (60%) incidence of aneurysmal bone cyst component in the hypovascular group. Hyperemic synovium, occasionally simulating tumor, was seen in 80% of surgically proved lesions. Angiography was useful in assessing tumor extent, particularly when an extraosseous component was present.