The ocular ischemic syndrome (OIS) has been reported in association with high-grade stenosis or occlusion of the common carotid artery (CCA) or internal carotid artery (ICA) but never with high-grade stenosis or occlusion of the external carotid artery (ECA) alone. We describe two patients who developed OIS with bilateral occlusion of the ECAs yet patent CCAs and ICAs. In one case, unilateral OIS followed consecutive bilateral carotid endarterectomies. In the other case, OIS developed spontaneously OU but was exacerbated in one eye after ipsilateral carotid endarterectomy (CE) in the setting of pre-existing contralateral ECA occlusion. In some individuals, the ECA is the primary source of arterial blood flow to the eye. Because of this fact, the endarterectomy surgeon must avoid causing ECA occlusion by meticulously removing not only the ICA plaque, but also the entire ECA plaque.