Hypothyroidism is a generalized hypometabolic syndrome caused by a relative or absolute deficiency of thyroid hormones due to various causes. There are many ways to classify hypothyroidism: primary, central, and peripheral, depending on the location of the lesion. Primary hypothyroidism is caused by a lesion in the thyroid gland itself and is called primary hypothyroidism. Central hypothyroidism is the absolute underproduction of thyroid hormone due to hypothyroidism caused by various causes of pituitary or hypothalamic hypofunction. It is mostly seen in the preoperative or postoperative period of external pituitary irradiation, pituitary macroadenoma, craniopharyngioma and other saddle area tumors. Hypothyroidism due to impaired peripheral action of thyroid hormones is mainly caused by reduced or defective thyroid hormone receptors in peripheral tissues, circulating antibodies to thyroid hormones or reduced conversion of peripheral T4 to T3. According to the cause of the lesion, hypothyroidism can be classified as pharmacological hypothyroidism, post-surgery or post-131I treatment hypothyroidism, idiopathic hypothyroidism and post-operative pituitary tumor hypothyroidism. Classification according to the degree of hypothyroidism can be divided into clinical hypothyroidism and subclinical hypothyroidism. Therefore, hypothyroidism is not one disease, but a group of diseases with many factors and many types of thyroid hormone deficiency as a common feature. Although the symptoms of different causes and types of hypothyroidism are similar, the treatment and prognosis are not the same.