To previously described causes of pseudo-occlusion of the internal carotid arteries, we have added an additional cause, that is, a tightly stenotic internal or common carotid artery reducing flow so as to not permit an adequate amount of contrast material to enter the vessel, thus giving the erroneous impression of total occlusion on the arteriogram. Four patients with cerebral ischemia were found to have apparent occlusion of a carotid artery by angiography. The internal carotid artery was involved in three instances and the common carotid artery in one case. Anatomic patency was discovered at the time of exploration and normal blood flow was restored by bifurcation thromboendarterectomy. Appreciation of this phenomenon will alert one to the possibility of anatomic patency and hence operability in spite of an apparent angiographic occlusion.