Hashimoto's encephalopathy (HE) is not an often complication of autoimmune thyroiditis, usually at the time the patient is already euthyroid i.e. with normal TSH-value but positive antibodies to thyroid hormones. Signs and symptoms are acute or sub-acute, such as cerebrovascular accident, epileptic seizures generalised, myoclonic or partial, cognitive function disorder with dementia and psychical disorders. Pathological findings, even non-specifical, can be found in cerebrospinal fluid, by electroencefalography (EEG) or by brain scan with magnetic resonance (MR). Pathogenesy of the disease is unclear; however, corticoid treatment is usually succesful. Therefore, HE should be taken into consideration after elimination of all other causes of encephalopathy, with thyroiditis in family history in particular.