A cohort of 10 Hashimoto's encephalopathy (HE) patients, 33 patients with unrelated neurological symptoms, 12 Hashimoto's thyroiditis patients and 4 healthy adult donors was studied to explore the neurological targets of anti-thyroperoxidase (TPO) autoantibodies (aAb) in HE. High levels of anti-TPO aAb were only detected in HE group's cerebrospinal fluids. In immunofluorescence assays on monkey brain cerebellum sections, both HE patients' sera and anti-TPO monoclonal antibodies (mAb) were able to bind cerebellar cells expressing glial fibrillary acid protein. Normal human astrocytes from primary cultures also reacted with anti-TPO mAb. Specific astrocyte binding of anti-TPO aAb suggests a role of these aAb in the HE pathogenesis.