Cerebral angiography often cannot distinguish between complete thrombosis or fibrosis of the internal carotid artery (ICA) and nonvisualization due to a total occlusion of the common carotid or origin of the ICA. Whereas surgery may be beneficial if the distal carotid is patent (type 1), thromboendarterectomy may be contraindicated if thrombus or fibrosis extend to the intracranial branches (type 2). Rapid sequential computerized tomography (RSCT) was used to examine 15 patients whose ICAs appeared occluded by angiography. Of four ICAs classed as type 1 by RSCT, three were found to be patent during surgical exploration, and carotid reconstruction was successfully performed. Three other ICAs classed as type 2 by RSCT were also surgically explored, and complete thrombosis was confirmed. The RSCT technique provides an effective and nonoperative means of determining whether a nonvisualized ICA is reconstructible.