Prevention of postoperative pain in children is one of the most important objectives of the anesthesiologist. Opioids have been used as an analgesic for postoperative pain in children for many years. Tramadol has both opioid and monoaminergic agonist actions. The aim of the study was to determine if the analgesic potency and occurrence of adverse effects of tramadol differ from pethidine when administered to children. A total of 110 healthy children, aged 2-12 years, scheduled for elective lower abdominal surgery were randomized to receive either pethidine 1 mg/kg (Group I, n = 60) or tramadol 2 mg/kg (Group II, n = 50) for postoperative pain after anesthesia induction. Pain intensity, adverse effects, heart rate, and systolic and diastolic blood pressure were recorded at regular intervals. The mean pain scores on postoperative 24 h were significantly greater with tramadol than with pethidine. Sedation scores, heart rate and systolic and diastolic blood pressure showed no significant differences between the groups. We conclude that pethidine and tramadol are effective in providing analgesia in pediatric patients, but pethidine provided better postoperative analgesia than tramadol. Changes in blood pressure, heart rate and arterial oxygen saturation were minimal and were similar in both drugs.