Abstract/Text: Sporadic spinocerebellar ataxias (SCAs) comprise heterogeneous diseases with poorly understood epidemiologies and etiologies. A population-based epidemiological analysis of sporadic ataxias in the Japanese population was described. The prevalence rate of SCAs in the Japanese population is estimated to be 18.5/100,000. Sporadic SCAs account for 67.2% of total SCAs including hereditary SCAs, with olivopontocerebellar atrophy (OPCA) being the most common form sporadic ataxia (64.7%). The natural history analysis conducted on the basis of International Cooperative Ataxia Rating Scale (ICARS) showed that only 33% of patients with OPCA were able to walk at least with one stick 4-5 years after the onset of OPCA, which is much less than that of patients with cortical cerebellar atrophy (CCA). Similarly, 43% of patients with OPCA were able to stand alone 4-5 years after the onset, while 76% of patients with CCA were able to stand alone at the same disease duration. A population-based epidemiological analysis should provide essential information on the natural history of SCAs.