A 91-year-old man presented with the sudden onset of coma, vertical gaze paresis, and transient disturbance of horizontal gaze, with fixed but unequal pupils. Both cranial computed tomography and postmortem study documented infarction of the paramedian thalamus bilaterally and of the ventral mesencephalon, accounted for by presumably embolic occlusion of a single artery. This artery arose as an unpaired perforating artery originating from the proximal segment of one posterior cerebral artery and thus conformed to the variant anatomic configuration associated with such infarcts as described by Percheron.