Unlike the rest of the brain or the spinal cord, the cerebellum may exhibit a condition rather common in this organ and collectively classified as atrophy. Cerebellar atrophies are for the most part secondary to some inflammatory, degenerative or vascular disease process, in contrast to agenesis, malformations, maldevelopments or aplasia, in which the atrophy is primary. Of the numerous classifications of cerebellar atrophies, that proposed by Marie, Foix and Alajouanine1 seems to me the most rational. These authors recognize three large groups: (1) congenital atrophies, which occur mainly in idiots and usually affect the lateral lobes of the cerebellum; (2) familial atrophies, represented by the cerebellar heredo-ataxia of Marie, and (3) a large group of acquired cerebellar atrophies, with which are included the olivopontocerebellar type of Dejerine and Thomas, the atrophy of the dentate system of Ramsay Hunt, and a type variously described and termed by them late cerebellar