Extradural clonidine produces analgesia in adults. To assess its efficacy in children, we randomized 45 pediatric patients aged 1-7 yr presenting for a subumbilical surgery into three groups of 15 each. After halothane and N2O/O2 induction, and with a double-blind protocol, caudal anesthesia was performed with 1 mL/kg of 0.25% bupivacaine. Epinephrine 1/200,000 was added in one group (EG), 1 microgram/kg of clonidine in another group (CG), and no additional medication in the last group (BG). Postoperative analgesia was evaluated using the Broadman "objective pain/discomfort scale" (OPS) at 1-h intervals until the first analgesic administration. There were no differences among the groups in age, weight, duration of surgery, baseline systolic arterial pressure, and heart rate. The mean (+/- SD) duration of analgesia was longer in the CG (987 +/- 573 min) than in the EG (377 +/- 341 min) and BG (460 +/- 439 min); P < 0.01. The maximal OPS scores were lower in the CG than in the EG and BG (2.3 +/- 1.6 vs 3.4 +/- 1.4 and 3.4 +/- 1.8, respectively; P < 0.05). More patients in the CG (n = 7) than in the EG (n = 1) and BG (n = 2) required no postoperative analgesia; P < 0.05. No differences were found among the groups for the minimal respiratory rate and minimal Spo2 values in the postoperative phase, and there were no differences among the groups for heart rate and systolic arterial pressure during the 3 h after caudal anesthesia. We conclude that the duration of postoperative analgesia with caudal bupivacaine was significantly increased by the addition of 1 microgram/kg of clonidine.