We report a patient who presented with a painful pupil-involving third-nerve palsy. Cerebral angiography revealed a high-grade stenosis of the ipsilateral internal carotid artery with a 4-cm intraluminal thrombus. Following emergent carotid endarterectomy, the patient's partial third-nerve palsy resolved in 1 hour. A pupil-involving third-nerve palsy may be an unusual presentation of impending carotid occlusion.