Introduction: Hashimoto encephalopathy is a rare encephalopathy with positive antithyroid antibodies and normal thyroid function. We describe the clinical manifestations, neuroimaging, and histopathologic changes in a 52-year-old female with Hashimoto encephalopathy. Results: The neuroimaging changes are multifocal abnormalities in cortical and subcortical areas bilaterally not enhanced by gadolinium. After high doses of corticosteroid therapy, the changes rapidly disappeared with marked improvement of clinical symptoms. Conclusions: This case shows the importance of assessment of antithyroid antibodies in patients with rapidly progressive cognitive dysfunction with/without the history of abnormality of thyroid function.