A patent internal carotid artery (ICA) is essential in most patients. Management of skull base lesions often requires translocation, balloon embolization, or resection of this vessel. Preoperative tests to assess the availability of collateral flow have not been uniformly accurate. A new test that significantly increases the safety of surgical removal of the ICA is described. One hundred thirty-six patients were studied with temporary balloon occlusion (TBO) of the ICA and determination of stable xenon-enhanced computed tomography cerebral blood flow (Xe/CT CBF) measurements. Eleven patients failed TBO and were determined to be at very high risk of stroke with loss of the ICA. Ninety-six of the patients were predicted to be at minimal risk with permanent loss of the ICA by Xe/CT CBF studies. Twenty-one patients in this group had either permanent balloon occlusion (PBO) or surgical resection of the ICA with no permanent neurologic sequelae. Our studies show that the combination of preoperative TBO and Xe/CT CBF studies significantly increases the safety of ICA resection.