Although cerebellar infarction was known at the turn of the century, not until 1956 was it realized that large cerebellar infarctions could cause acute obstructive hydrocephalus. There are many more reports of cerebellar hemorrhages. The clinical differentiation between hemorrhage and infarction was difficult prior to computerized tomography (CT). Cerebellar hemorrhage is a neurosurgical emergency, as are some cerebellar infarctions. We present three patients with acute hydrocephalus resulting from these vascular syndromes; they are the first cases to be successfully treated by ventricular drainage and shunting. Four other cerebellar infarcts demonstrate the efficacy of CT.