Recently, we discovered autoantibodies against the amino (NH(2))-terminal of alpha-enolase (NAE) in patients with Hashimoto's encephalopathy (HE) (83.3%; 5/6) [Fujii, A., Yoneda, M., Ito, T., Yamamura, O., Satomi, S., Higa, H., Kimura, M., Suzuki, M., Yamashita, M., Yuasa, T., Suzuki, H., Kuriyama, M., 2005. Autoantibodies against the amino terminal of alpha-enolase are a useful diagnostic marker of Hashimoto's encephalopathy. J. Neuroimmunol. 162, 130-136]. We further investigated the anti-NAE autoantibodies in 25 patients who fit the diagnostic criteria for HE, based on the presence of anti-thyroid antibodies and responsiveness to immunotherapy. In this study, we demonstrated a high prevalence (68%, 17 of 25) and high specificity of anti-NAE autoantibodies in patients with HE, and clarified the clinical features of HE. This result demonstrated that anti-NAE autoantibodies, in addition to anti-thyroid autoantibodies, are emphasized as useful serological diagnostic markers of HE.