BACKGROUND: Adenotonsillectomy is one of the most common surgical procedures in children. Several complications and morbidities are common after nasal surgeries and the most common is pain. Several techniques have been employed to reduce the severity of postoperative pain. One of the preoperative techniques is pre-emptive analgesia through preventive central hypersensitization. This technique is performed by applying analgesic methods before the onset of nociceptive stimuli, consequently decreasing postoperative analgesics requirements. OBJECTIVES: Preoperative oral drug administration for pain analgesia is performed in several methods. The aim of this study was to compare the analgesic effects of preoperatively administration of oral acetaminophen and ibuprofen. PATIENTS AND METHODS: In a double-blinded, randomized placebo-controlled study, sixty 4-12 years old ASA I or II children scheduled for elective adenotonsillectomy, were assigned to receive either acetaminophen 15 mg/kg, ibuprofen 10 mg/kg or placebo 30 minutes before the operation. Postoperative pain was assessed using the Children's Hospital of Eastern Ontario Pain Scale (CHEOPS), upon arrival to the post anesthetic care unit (PACU) and ward. Findings were analyzed by SPSS version 17 using variance analysis and Tukey's test. RESULTS: The average pain intensities were significantly lower in acetaminophen group based on the CHEOPS in both PACU and ward compared to ibuprofen or placebo groups; but there was no difference in pain intensity between the ibuprofen and placebo groups. Pain intensity in PACU in Acetaminophen group was 7.05 ± 0.64 vs. 8.38 ± 1.20 in placebo group and 8.14 ± 0.85 in ibuprofen group, pain intensity in ward in the acetaminophen group was 6.0.87 ± 0.85in the acetaminophen group, vs. 8.04 ± 1.02 in placebo group, and 7.78 ± 0.78 in ibuprofen group. CONCLUSIONS: This study showed that administration of oral acetaminophen 30 minutes preoperatively, resulted in significantly lower pain intensity in children undergoing adenotonsillectomy in PACU and ward, compared to ibuprofen and placebo.