OBJECTIVE This study was designed to evaluate the analgesic efficacy of caudal midazolam-bupivacaine combination in providing post-operative pain relief in children undergoing genitourinary surgery and to study the occurrence of adverse effects. METHODS Thirty children, aged 2 to 8 years, scheduled for genitourinary surgery were allocated randomly to receive either 0.25% bupivacaine 0.5 ml/kg (group B; n = 15) or 0.25% bupivacaine 0.5 ml/kg with 50 microg/kg midazolam (group BM; n = 15) by the caudal route immediately after induction of general anesthesia. Heart rate, arterial blood pressure and oxygen saturation were monitored throughout the study period. Postoperative pain was assessed at regular intervals for 12 hours using an objective pain score. Analgesia was supplemented whenever the pain score was > or = 4. Duration of analgesia, as well as the requirement of additional analgesics, were noted. RESULTS Lowest pain scores were observed with the addition of midazolam to caudal bupivacaine (p < 0.01). Duration of analgesia was longer in group BM (11 +/- 0.5 h) as compared to group B (7.4 +/- 2.1 hours) (p < 0.05). Fewer children (26.6%) required additional analgesia in the combination group whereas in group B, 60% of the children received analgesic supplements within 6 hours after surgery (p < 0.05). There were no significant changes in heart rate, blood pressure and oxygen saturation in both groups. We observed no untoward event in either of the groups. CONCLUSIONS Caudal administration of bupivacaine-midazolam mixture prolongs post-operative analgesia compared to bupivacaine alone without causing any adverse effects.