The classifications of hereditary ataxias (HA) proposed from 1907 to 1984 are reviewed. An analysis is provided of the possible variables in the classification of HA, including inheritance, known metabolic or other cause, localization of pathological lesions, clinical signs, natural history, epidemiology, diagnostic tools. Harding's classification is assumed to be the best clinical tool to support molecular genetics studies. However, we suggest the inclusion of Late Onset Recessive Cerebellar Ataxias in Harding's classification. Some exceptions must be considered for the diagnostic criteria of Friedreich's disease. Early Onset Cerebellar Ataxia with retained tendon reflexes (EOCA) is probably a heterogeneous entity.