In a previous communication on the syndrome of the superior cerebellar artery,1we called attention to the nature of cerebellar vascular occlusion and its rarity in contrast to cerebral vascular insults. At the time in only twenty such cases in our series of over three hundred was involvement of the cerebellar arteries revealed. In five of these cases the occlusion was confined to the posterior inferior cerebellar artery, and in one, to the anterior inferior cerebellar artery. Of all the cerebral and cerebellar vessels, anomalies are most commonly observed in the posterior inferior cerebellar artery. The variability of symptoms in cases of lesions of this artery is explainable on this basis. For a better understanding of the lesions and their anatomic relations, a brief description of the distribution of the inferior cerebellar vessels is given. Posterior Inferior Cerebellar Artery. —This vessel arises from either the vertebral or the basilar