BACKGROUND Transient renal failure during surgery is caused by increasing secretion of stress hormone such as ADH and renin. We suspected that urinary output varies according to administration of remifentanil with potent analgesic effects. Consequently, we studied intraoperative urinary output of two groups, patients administered with remifentanil and those without remifentanil administration. METHODS We compared urinary output during general anesthesia, of 327 patients administered with remifentanil (Group R) and 314 patients without remifentanil administration (Group NR) retrospectively. Patients were excluded if they were under the age of eighteen, receiving epidural anesthesia, or having medicine with diuretic effect. RESULTS There were no significant difference in background of the patients in each group, in particular, age, sex, body weight, and ASA grade. We found no significant difference in intraoperative factors; operation time, total blood loss, volume of infusion, anesthesia time, and given dose of fentanyl. Urinary output of Group R was estimated as 512 +/- 435 ml, and that of Group NR was 409 +/- 405 ml (P value was 0.02). CONCLUSIONS We found a significance difference in urinary output during anesthesia, between patients administered with remifentanil and those without remifentanil administration. We suspect that remifentanil decreases urinary output in the perioperative period.