Background: Patient-controlled analgesia (PCA) has proven to be safe and effective in children from age 5 years, and older and compares favourably with continuous morphine infusion in the older child. We compared fentanyl and butorphanol for opioid use in PCA with ketorolac to determine a suitable drug combination for post-tonsillectomy pain control. Methods: We studied 60 patients, aged 5-12 yrs, undergoing tonsillectomy with or without ade- noidectomy under general anesthesia using N2O-O-enflurane. Patients were randomly assigned to receive fentanyl 250 μg (Group 1: n-30) or butorphanol 5 mg (Group 2: n-30) mixed with ketorolac 90 mg and ondansetron 4 mg diluting l00 ml of 5% D/W solutions intravenously via PCA pump after operation. PCA pump were programmed to deliver a 0.05 ml/kg loading dose, 0.01 ml/kg/hr basal infusion, 0.01 ml/kg on demand bolus, 6 min lockout intervals between doses and 4 bolus hourly limit. Total infusion dosage of PCA drug, VAS pain scores, side effects and satisfaction score of both groups were monitored for 48 hrs. Results: Total infusion dosages were fentanyl 170.6 pg with ketorolac 61.4 mg (Group 1) and butorphanol 2.8 mg with ketorolac 50.4 mg (Group 2). Total infusion dosage, quality of analgesia, side effects and overall satisfaction didn't differ between two groups. Conclusions: Both fentanyl and butorphanol mixed with ketorolac were effective for post-tonsillectomy pain control using PCA pump in children as young as 5 years old.