Eight patients with Pierre Mary hereditary cerebellar ataxia were followed for several years in four generations of a family. Clinical pictures in those afflicted were stereotype: step-by-step increase of cerebellar and brainstem disorders, reduction of intellect, enforced tendon and periosteal reflexes with extrapyramidal and pelvic disorders absent even in the far developed cases. A strict autosome-dominant type of inheritance was demonstrated with no one generation escaped. Analysis of clinical signs suggests the nosologic separateness of the disease. The issues of its differentiation with several other forms of hereditary disorders are discussed.