BACKGROUND: For outpatient pediatric anesthesia, pain has perhaps been the main cause of hospitalization. Caudal blocks have been used to treat postoperative pain after low abdominal surgery. The purpose of this study was to evaluate and compare the analgesic effect and the incidence of side effect of caudal bupivacaine alone, a bupivacaine-morphine mixture, and intravenous ketorolac in pediatric day surgery patients. METHODS: Forty three patients, aged 1 to 7 years, were divided into three groups after the induction of general anesthesia. Caudal blocks were performed with 0.2% bupivacaine 0.7 ml/kg alone (group B), 0.2% bupivacaine 0.7 ml/kg and morphine 0.03 mg/kg (group M), and normal saline 0.7 ml/kg (group K). Ketorolac 0.8 mg/kg (group K) or normal saline 2 ml (group B and M) was injected intravenously before incision. Postoperative pain/discomfort scales and 4-point patient sedation scores were assessed, and the incidences of side effects were observed after recovery. RESULTS: Pain/discomfort scores in the group B and K were significantly greater than in group M. There was no difference among the groups in the 4 point patient sedation score. The incidences of nausea/vomiting and urinary retention were more frequent in group M but discharge was not delayed by the side effect. CONCLUSIONS: The addition of morphine to bupivacaine for caudal block provides more effective postoperative analgesia than caudal block with bupivacaine alone and intravenous ketorolac administration in day surgery. Side effects such as nausea/vomiting and urinary retention must be considered after use of morphine during caudal block.