To determine the frequency of cerebellar ataxia patients with autoantibodies for Hashimoto's disease, we analyzed 68 patients who were examined serum test for autoantibodies of Hashimoto disease among 178 cerebellar ataxia patients who visited our neurology clinic from January 2005 until December 2007. In these 68 patients, 8 had autoantibodies for Hashimoto's disease. Five of these 8 patients were diagnosed with hereditary spinocerebellar ataxia by genetic analysis. Moreover, one patient was diagnosed with probable multiple system atrophy by neurological examination. Cerebellar ataxic disease of known causes was ruled out for the remaining two cases; they were euthyroid and their cerebellar ataxia was slowly progressive and were diagnosed with cortical cerebellar atrophy. Although Hashimoto's disease may associate with cerebellar ataxia because cortical cerebellar atrophy is a heterogeneous condition, this association is not clear at present.