Background: Hashimoto’s encephalopathy (HE) presents with a variety of neurologic and neuropsychiatric features. In this study, we investigated the clinical and immunological profiles of the cerebellar ataxic form of HE. Methods: The clinical features, treatments, laboratory features, brain imaging, and serum anti-NH2-terminal of α-enolase autoantibodies (anti-NAE Abs), a useful diagnostic marker for HE, were investigated in 13 patients who presented with sporadic adult-onset cerebellar ataxia and fulfilled the HE diagnostic criteria (antithyroid Abs and responsiveness to immunotherapy). Results: All of the patients presented with truncal ataxia, but nystagmus was uncommon (17%). Eight patients had an insidious onset that mimicked spinocerebellar degeneration (SCD), but brain imaging showed little or no cerebellar atrophy in all of the patients. Those patients with serum anti-NAE Abs (n = 8) did not have nystagmus and tended to respond better to immunotherapy than the anti-NAE Ab-negative patients. Conclusion: The present study suggests that insidious adult-onset and truncal ataxia are common in the cerebellar ataxic form of HE, which mimics SCD, but that nystagmus and severe cerebellar atrophy are uncommon. Antithyroid and anti-NAE Abs may be useful for diagnosing cerebellar ataxic HE.