Hashimoto's encephalopathy (HE) is a rarely recognized neurocognitive syndrome that is associated with thyroid autoimmunity. It is more common in women. HE is diagnosed when patients present with nonspecific neurological symptoms associated to elevated titers of antithyroid antibodies and normal or abnormal thyroid function tests. Other neurologic disorders must be ruled out before diagnosis can be established. HE is associated to nonspecific EEG abnormalities as well as elevated cerebrospinal fluid proteins and nonspecific white matter changes. The pathophysiology of HE is unknown but an autoimmune etiology is strongly supported. HE responds to corticosteroids and immunosuppressive therapy, further supporting an autoimmune etiology. A high index of clinical suspicion must be present in order to promptly recognize and treat this disease.