Summary:Hashimoto's encephalopathy is a rare brain disease.Its etiology is still unknown.In this paper,we reported a 15-year-old female patient underwent total thyroidectomy and lymph node dissection,due to a multifocal papilliferous carcinoma of the right lobus.Forty-two days after surgery,the patient was treated by 131I radiotherapy in another hospital and begun to have a headache after 48 hours.At last,the patient was diagnosed by HE on the basis of all considerations.She recovered from by i.v.Immunoglobulin.Till now,the patient has not relapsed for more than 4 years follow-up.