Hashimoto encephalopathy is a chronic relapsing steroid responsive encephalopathy characterized by antibodies against thyroid components. Etiology is still unknown. Confusion, seizures and coma are frequent reported symptoms. We present a 65-year old patient with acute onset of partial seizures and cognitive impairment. Hashimoto encephalopathy was assumed with diagnosis of Hashimoto thyroiditis and clinical syndrome. Symptoms resolved with thyroid treatment alone. Hashimoto encephalopathy should be considered in patients with unexplained encephalopathy, even when thyroid function seems to be normal.