The thyroid gland is a small butterfly-shaped organ located in the neck in front of the trachea. It is an endocrine organ that synthesizes and secretes thyroid hormones. So what does thyroid hormone do? Thyroid hormones are synthesized and secreted into the bloodstream, and transported with the blood to various tissues of the body. They are mainly responsible for the body’s energy metabolism, maintaining body temperature, and ensuring the normal functioning of important tissues such as the brain, heart, and muscles. Iodine is the most important raw material for the synthesis of thyroid hormones. Iodine deficiency can lead to insufficient synthesis of thyroid hormones, and almost all organs and tissues of the body will be affected. Hong Zhang, Department of General Surgery, The Second Hospital of Jilin University The most common diseases of the thyroid gland are as follows: 1. abnormal thyroid function-hypothyroidism and hyperthyroidism; 2. goiter; and 3. thyroid tumors-benign and malignant. In the following articles, we will introduce each of these diseases one by one.