To test the hypothesis that preoperative head computed tomography scans could be used to predict the likelihood that a patient with a supratentorial brain tumor would develop intracranial hypertension during surgery before the cranium was opened, intraoperative intracranial pressure and blood pressure records of 60 patients undergoing craniotomy were compared with the appearance of their preoperative computed tomography scans. The scans were interpreted by a neuroradiologist who was unaware of the clinical events in each case. A positive correlation was found between the amount of preoperative brain edema observed surrounding tumors (on an arbitrary 0 to 3 + scale) and subsequent increases in intracranial pressure greater than base line values. No such correlation could be found with regard to tumor size, shift of midline structures, or effacement of the lateral ventricles. When preoperative brain edema seen on computed tomography scan was taken into consideration, increases in intracranial pressure during craniotomy also correlated with simultaneous increases in blood pressure. It is concluded that patients with large amounts of preoperative brain edema surrounding supratentorial tumors should be considered at risk for developing intraoperative intracranial hypertension and may benefit from preoperative insertion of an intracranial pressure monitor before general anesthesia is induced.