Horner's syndrome has important localizing and etiological value in acute ischemic stroke. In a prospective series of consecutive acute ischemic stroke patients, we identified three patients with Horner's syndrome and contralateral hemiparesis due to ipsilateral small deep infarction in the middle cerebral artery territory (lenticulostriate arteries). Lacunar stroke was the most likely stroke mechanism in all three patients. This observation might suggest the existence of an uncrossed cortico-hypothalamic sympathetic pathway passing through the basal ganglia and modulating oculosympathetic function.