63 patients with primary cerebellar and spinocerebellar ataxia have been studied with MRI. This method allows to identify in vivo different groups of diseases such as that characterized by atrophy of cerebellum alone; that with atrophy of cerebellum associated with brainstem changes; the forms with associated changes of basal ganglia; the forms with spinal cord atrophy alone, as well as transitional forms. An interesting correlation between the varying groups and the type of inheritance was found, while no correlation with other clinical aspects was observed.