Sixteen patients with upper tract urothelial carcinoma underwent intravesical chemotherapy usually at 2 week intervals in the first year and at 4 week intervals in the second year after nephrouretectomy. For bladder instillation 10 mg mitomycin C in 20 ml saline was used on 7 patients, 5 mg carboquone and 100 mg cytosine arabinoside in 40 ml saline on 5 patients and 30 mg adriamycin in 40 ml saline on 4 patients. Two (12.5%) of the 16 patients developed bladder tumors within 2 years after surgery, but 11 (42.3%) of the 26 patients with upper tract urothelial carcinoma who did not receive intravesical chemotherapy suffered from bladder tumor within 2 years after surgery. Prophylactic intravesical chemotherapy reduced significantly (p less than 0.1) the incidence of bladder tumor after the surgery of renal pelvic and ureteral tumors.