The pattern of arterial occlusion and related lesions have been studied in 26 cases with 38 medullary infarcts. In 10 of these cases, only the intracranial vessels were examined. In the 16 other cases, the entire cerebral arterial supply was dissected. Medial infarcts were more often related to occlusion of the vertebral artery involving the termination of the artery ( 7 10 cases). In 6 cases a thrombosis on an atheromatous plaque and, once, an embolus of cardiac origin, were found. Lateral infarcts were usually due either to occlusion of the vertebral artery ( 14 23 cases), reaching, in 10 cases, the mouth of the posterior inferior cerebellar artery (PICA) or to an isolated occlusion of the latter vessel (3 cases). A thrombosis on an atheromatous plaque was found in 15 cases, and emboli from the heart or from the origin of the vertebral artery in the others. The dorsal infarcts were related, in 4 5 cases, to an isolated occlusion of the stem of the PICA and, in the other case, to one of the vertebral artery involving the ostium of the PICA. A thrombosis due to atheromatous stenosis was found in 4 cases, an embolus of cardiac origin in the other one. © 1976.