Between November 1994 and July 1996, 45 patients with superficial bladder tumor were assigned to two groups before transurethral resection of bladder tumor. Twenty-one of the 45 patients were instilled with 20 mg epirubicin before endoscopic resection then continuously irrigated with 40 micrograms/ml epirubicin solution for 20 hours immediately after surgery; 24 of the 45 patients received continuous irrigation with saline in the same manner. The patients were assessed by cystoscopy and urinary cytology every 3 months during the first 2 years and every 6 months thereafter. One year recurrence-free rates in the treated and control groups were 56% and 32%, respectively. The recurrence-free period tended to be longer in the treated group than in the control group, although the difference was not significant (p = 0.17). One year recurrence-free rates in the treated and control groups for the patients with solitary tumor were 88% and 48%, respectively, the difference being marginally significant (p = 0.06). These results suggested that continuous bladder irrigation with epirubicin was effective for patients with a single tumor. Therefore, the long-term prophylactic therapy for a single tumor was an overtreatment. Prophylactic intravesical chemotherapy for superficial bladder cancer was proposed to be stratified by the number of tumors, single or multiple.