Abstract In a study of 50 patients who had undergone prostatectomy the incidence of deep-vein thrombosis was measured, using the 125I-fibrinogen test. Of these, 12 (24 per cent) developed deep-vein thrombosis. This preliminary study showed that in patients who had had a transurethral resection the incidence of deep-vein thrombosis was 6·8 per cent, while in patients who had had a retropubic prostatectomy it was 47·6 per cent.