BACKGROUND: The use of caudal morphine for postoperative analgesia has been increased in popularity since 1981. The purpose of this study was to compare the effect of analgesia and incidence of side effects of a mepivacaine-morphine mixture with mepivacaine alone. METHODS: Forty patients were randomly divided into two groups. In group 1, caudal block was performed with 1% mepivacaine 1 ml/kg alone. In group 2, caudal block was performed with 1% mepivacaine 1ml/kg-morphine 0.03 mg/kg mixture. Postoperative five-point pain scores and side effects were measured. RESULTS: There were no significant differences in sedation dose, incidence of side effects and supplemental analgesics. Pain scores were significantly lower at postoperative 2 and 3 hours in mepivacaine-morphine mixture group. CONCLUSIONS: Caudal epidural mepivacaine-morphine (0.03 mg/kg) mixture is effective in children for control of postoperative pain without significant side effects.