As definite, independent morbid entities, atrophies of the cerebellum are probably more common than inflammations, degenerations or tumors of this organ. Like tumors, cerebellar atrophies may be circumscribed, and like inflammatory or degenerative conditions they may be concomitant manifestations of atrophies elsewhere in the central nervous system. The best known and fairly well studied form of cerebellar atrophy has been described as tardy or late atrophy, predominantly of the cerebellar cortex (Marie, Foix and Alajouanine1). It is also known as sclerotic atrophy of the cerebellum, as lamellar and primary parenchymatous cerebellar atrophy and by other names.2 Atrophies of the cerebellum that are associated with atrophies elsewhere in the central nervous system are represented by a number of pathologic entities of which the best known are crossed, olivopontocerebellar and olivorubrocerebellar. However, they cannot be differentiated clinically, though pathologically they are fundamentally alike, differing from one another only in the