Hashimoto’s thyroiditis, so named because it was first proposed by the Japanese Hashimoto in 1912. It is also known as chronic lymphocytic thyroiditis because of the microscopic infiltration of lymphocytes in the thyroid gland of patients with this disease. It is now clear that this disease belongs to the category of autoimmune diseases and is classified as an autoimmune thyroid disease along with hyperthyroidism. Autoimmune disease is a condition in which the body’s immune system (lymphocytes) mistakes its own tissues, such as the thyroid gland, for foreign objects and causes inflammation, etc. The prevalence of the disease is about 2% and is most common in middle-aged women, 5 to 10 times more often than in men. The causes of Hashimoto’s thyroiditis are twofold: one is internal, i.e., genetic. The disease has a family tendency to run in families, and it is often possible to ask if one of the patient’s siblings or parents or uncles has thyroiditis or hyperthyroidism. The other is an external factor, namely environmental factors, mainly increased iodine consumption. The reason for the dramatic increase in the incidence of Hashimoto’s thyroiditis in recent years is thought to be related to the universal over-iodization of salt. The disease is the most common cause of goiter and hypothyroidism (hypothyroidism or low thyroid) in children and adolescents. Hashimoto’s thyroiditis affects the body in two main ways. One is an enlarged thyroid gland, mild to moderate, which usually does not cause neck compression symptoms such as shortness of breath or difficulty swallowing. It is firm and rubbery to the touch, with no pain or pressure. Some patients with Hashimoto’s thyroiditis can neither see nor feel the enlarged thyroid gland. Second, Hashimoto’s thyroiditis can cause hypothyroidism. Mild hypothyroidism can be asymptomatic. Overt hypothyroidism can be characterized by fear of cold, swelling, anemia, weakness, decreased appetite, rough and yellow skin, slowed heart rate, and excessive menstrual disorders in women. Because it is a chronic disease with an insidious onset, thyroid function at the time of initial diagnosis can be normal, or it can manifest as mild or severe hypothyroidism. In recent years, as living standards have improved, health care has become more important, and health insurance has become more widespread, thyroid function is often normal in patients with initially diagnosed Hashimoto’s thyroiditis. The diagnosis of Hashimoto’s thyroiditis relies mainly on laboratory tests. A positive TPOAb is more common than a positive TgAb and has a higher titer and longer duration than a positive TgAb. The rate of positive TPOAb is over 80% and the rate of positive TgAb is 60%, and the rate of positive complementary results can be over 90% when both are measured. About 10% of the patients with negative antibodies can be diagnosed with the help of ultrasound or, if necessary, pathological examination by thyroid aspiration. Hashimoto’s thyroiditis is often underdiagnosed because some patients have no enlargement of the thyroid gland, most have insignificant enlargement, and hypothyroidism can be asymptomatic. A significant number of patients are detected during a health check-up. Special attention should be paid to screening for the disease in those with a family history or neck enlargement. Because even mild hypothyroidism can cause abnormalities in mother and child, special attention should be paid to screening for thyroid function and Hashimoto’s thyroiditis in pregnant women, and preconception screening is recommended. Although Hashimoto’s thyroiditis cannot be cured, it does not turn into thyroid cancer and has a good prognosis. The worst outcome is hypothyroidism, but there are good treatments for hypothyroidism. It is beneficial to reduce the consumption of seafood appropriately, but because it is difficult and even harmful to adhere to a low iodine diet for a long time, we believe that abstaining from seaweed and nori and eating less sea fish and sea shrimp is sufficient. On average, 2.5% of Hashimoto’s thyroiditis with normal thyroid function progress to hypothyroidism each year, so it is important and necessary to perform regular, such as annual, thyroid function measurements on patients. In recent years, studies have confirmed that supplementation with selenium such as selenium yeast can reduce the level of thyroid autoantibodies and may slow down the progression of the disease, so it can be applied appropriately. Hypothyroidism is treated with direct supplementation of thyroid hormones, mainly levothyroxine, which can easily ensure normal thyroid function, and the enlarged thyroid gland is also seen to shrink significantly after medication. It is worth mentioning that some doctors prescribe glucocorticoids such as dexamethasone and prednisone to patients with Hashimoto’s thyroiditis, both orally and by injection, which are not scientific.