Twelve resections of prostate and 1 extensive bladder tumour were performed in patients on long-term anticoagulation without withdrawal of warfarin therapy. The mean preoperative prothrombin index was 2.3. Four patients required blood transfusion. There were no major complications. The effects of surgery and infusion of fresh frozen plasma (FFP) on the level of anticoagulation were monitored. FFP reduced the prothrombin index by 0.25/unit. Transurethral resection can be carried out safely by an experienced urologist on patients anticoagulated with warfarin, reducing the risk of serious thromboembolic complications associated with withdrawal of anticoagulation.