Cerebral swelling and herniation pose serious surgical obstacles during craniotomy for space-occupying lesions. Positioning patients head-up has been shown previously to reduce intracranial pressure (ICP) in neurotraumatized patients, but has not been investigated during intracranial surgery. The current study examined the effects of 10-deg reverse Trendelenburg position (RTP) on ICP and cerebral perfusion pressure (CPP). Forty adult patients subjected to craniotomy for supratentorial tumors were given standardized propofol-fentanyl-cisatracurium general anesthesia and were moderately hyperventilated. In 26 of 40 patients with expected poor clinical outcome, an additional catheter was placed in the internal jugular bulb to determine internal jugular bulb pressure (JBP). ICP was determined by subdural measurement using a 22-gauge needle advanced through the dura after removal of the bone flap. ICP was referenced to the level of the dural incision. ICP, mean arterial blood pressure, and CPP were compared with repeat measurements 1 minute after RTP. The tension of the dura was graded qualitatively by the surgeon by digital palpation and was compared to post-RTP. ICP decreased from 9.5 mm Hg to 6.0 mm Hg ( P <.001; all values are median) within 1 minute after 10-deg RTP. Mean arterial blood pressure decreased from 82.0 mm Hg to 78.5 mm Hg ( P <.001). CPP was unchanged (70.5 mm Hg versus 71 mm Hg after RTP), whereas JBP decreased from 8 mm Hg to 4 mm Hg ( P <.001). High initial ICP was correlated to the greatest magnitude of decrease in ICP. No significant correlation was found between change in ICP and change in JBP. Intracranial pressure after RTP resulted in decreased tension of the dura. RTP appears to be an effective means of reducing ICP during craniotomy, thereby reducing the risk of cerebral herniation. CPP is not affected. Studies over longer periods of time are warranted, however.