This study was carried out to evaluate the effects of perioperative indomethacin on intracranial pressure (ICP). Forty patients subjected to craniotomy for supratentorial cerebral tumors were anesthetized with propofol, fentanyl and isoflurane. A PaCo2 level averaging 35-40 mmHg was achieved. The patients were randomized to intravenous indomethacin 50 mg as bolus then infusion by 0.3mg/kg/hr. till opening the dura in 20 patients or placebo administrated in the other 20 patients . ICP was measured continuously subdurally with ICP probe (Codman Micro Sensor, Johnson & Johnson Medical Ltd) A significant decrease in ICP from 9.5 to 2.6 mm Hg (median) was found after indomethacin administration. In the indomethacin group, dura was sufficiently relaxed and dura was opened without the occurrence of cerebral swelling. In the placebo group, mannitol supplemented with hypocapnia was applied in many patients. These findings suggest that perioperative treatment with indomethacin is an excellent treatment of intracranial hypertension during normocapnic isoflurane anesthesia for craniotomy.