Ophthalmoplethysmography (OPG) is a simple, noninvasive diagnostic test in which the cerebral hemispheric blood flow can be indirectly measured. Its use in head and neck surgery is invaluable because it enables the surgeon to predict preoperatively whether a patient will survive carotid artery resection. In a three-year period, nine patients have survived carotid resection on the basis of favorable OPGs, without a death or permanent neurologic complication. A comparison of the results of OPG testing with intraoperative measurement of internal carotid artery pressure showed close correlation in 14 of 20 patients who were tested. Lack of correlation in four patients can be explained by the circumstances of the intraoperative test. This study's findings demonstrate that this test has high clinical reliability.