Although old or recent infarcts of a cerebellar hemisphere in the territories of the posterior inferior (PICA), superior, or anterior inferior cerebellar arteries are commonplace autopsy findings, in no case have corresponding clinical symptoms been clearly identified. We have studied three cases, two clinocaopthologically and one clinicosurgically, in which an acute infarct involving only the cerebellum lay in the PICA territory distal to the branches to the medulla oblongata. The clinical manifestations consisted of rotatory dizziness intensified by motion, nausea, vomiting, imbalance, and nystagmus. In two cases, the clinical diagnosis had been a benign labyrinthine disorder. Recognition of a syndrome corresponding to cerebellar infarction in the PICA territory is important insofar as it assists in the differential diagnosis of dizziness. It becomes of crucial importance when cerebellar infarction is the prelude to cerebellar swelling and brain stem conpression leading to coma and death unless surgically relieved.