BACKGROUND: Postoperative pain control in children is a difficult problem for management. Fentanyl is one of the most commonly used narcotics in infants and children due to its rapid onset and brief duration. Infants older than 3 months had a lower incidence of apnea than adults given fentanyl; however, the dosage of fentanyl varies a great deal depending on the purpose and plan for the postoperative management. This study is designed to evaluate the effective dose of intraoperative intravenous fentanyl for pain control following inguinal herniorrhaphy in pediatric patients. METHODS: Sixty children for inguinal herniorrhaphy under general anesthesia were divided into four groups. Group I received no analgesics as a control. Group II, III and IV received intravenous fentanyl 0.5 microgram/kg, 1 microgram/kg and 1.5 microgram/kg respectively. Fentanyl was injected intravenously at the beginning of fascia closure. Extubation time and the degree of pain was evaluated. RESULTS: Our result showed that group III and IV had a lower pain score than that of the control group during the first 30 min in the recovery room (p<0.05), but no significant differences were found between the group III and group IV. The time interval from fascia closure to extubation was prolonged in the group II, III and IV compared to the control group (p<0.05). But no significant differences were found between the three groups. CONCLUSION: We suggest that intravenous administration of fentanyl 1 microgram/kg at the closure of fascia would be an easy, simple and effective means for relieving postinguinal herniorrhaphy pain in recovery room.