Cerebral ischemia resulting from carotid artery atherosclerosis is related most frequently to atherosclerosis of the proximal internal carotid artery (ICA). Cerebral ischemic symptoms associated with atherosclerosis of the external carotid artery (ECA) occur uncommonly and usually only when the ipsilateral ICA is occluded. This report documents a case of thrombosis related to ECA atherosclerosis causing a stroke due to embolism via a patent ICA. The case also illustrates the value of performing cerebral angiography in a patient without a clearly identified cause of stroke.