There is no chapter of neurology and neuropathology which is more contradictory than that on the cerebellar ataxias. Strictly speaking, there are three types: (1) the heredocerebellar ataxia of Pierre Marie; (2) the olivopontocerebellar ataxia of Dejerine and Thomas, and (3) the ataxia with cerebellar cortical atrophy. The classification and differentiation of these conditions are difficult because the same parts of the brain stem and cerebellum are frequently affected. The most important property of Marie's type is its outspoken hereditary tendency. This property justifies its classification as a separate entity. In this report we will consider only the hereditary form. I. CLINICAL AND PATHOLOGIC STUDY By Drs. Waggoner and Löwenberg REPORT OF CASE Well developed symptoms of the disease have been observed through five generations in 26 members of a white, American family of 180 members. History. —P. M., a man aged 42, was first seen on Feb. 18, 1933.