Ipsilateral mydriasis (IM) is usually not acute. However, the acute occurrence of unilateral dilated pupil may result in acute ischemic stroke. Herein, we present 3 patients with IM, lateral eye deviation, ptosis, and contralateral hemiparesis due to isolated occlusion of the pre-communicating segment of the posterior cerebral artery with preservation of the posterior communicating artery, which was successfully treated by emergent mechanical thrombectomy. In a 3-month follow-up, all patients were independent without any neurological deficits.