Male breast enlargement is called gynecomastia, with a prevalence of about 30%, which mostly occurs in male adolescence or old age. Its pathogenesis is related to a variety of endocrine hormone imbalances in the body, such as increased or relatively increased estrogen levels, or increased sensitivity of estrogen receptors in breast tissue to estrogen, or defective androgen receptors. It can be divided into two categories: primary and secondary. Primary cases include three types: 1. Infancy: Attributed to high maternal estrogen levels, which usually resolve on their own in 2 to 3 weeks. 2. Puberty: It occurs at the age of 13 to 14 years and usually subsides on its own after the age of 18. About 80% of them develop bilaterally, often forming a 2~3cm disk-shaped lump under the areola, and gradually developing, even reaching the size of female breast volume. 3, old age: the highest prevalence of 50 to 80 years old. It starts as an enlargement of one breast, often forming a 2~4cm lump under the areola with clear borders, and mostly fades naturally within 1 year. Secondary includes four types: 1. Gynecomastia secondary to hypogonadism. It is commonly seen in men with primary hypogonadism, but also in men with hypogonadism secondary to pituitary or hypothalamic lesions. 2. Gynecomastia secondary to tumors. Commonly seen in patients with testicular tumors, adrenal tumors, lung cancer, etc. 3. Gynecomastia secondary to systemic diseases (increased aromatase). Commonly seen in patients after hemodialysis treatment, impaired liver function, hyperthyroidism, hypoadrenalism, etc. 4. Medicated gynecomastia. Commonly seen in patients suffering from prostate hyperplasia who have been taking estrogen for a long time, patients suffering from gastric disease who have been taking methocarbamol for a long time, etc. In addition, many obese men have more fat content in their breasts, which can also manifest as bilateral breast enlargement and augmentation. Diagnosis: It is mainly based on medical history, physical examination and laboratory examination. Laboratory examination includes endocrine examination, liver and kidney function, thyroid function, testosterone and estrogen level, LH and FSH test, etc. The lump is hard, infiltrates into the surrounding tissues and has limited mobility. Treatment: 1. Watchful waiting, suitable for those with onset of gynecomastia less than 12 to 18 months, for adolescent gynecomastia physical examination including genitalia is performed and rechecked within 6 months. For drug-induced gynecomastia, re-evaluation is performed after a period of discontinuation of medication. 2.Medication for persistent gynecomastia, three types of drugs: androgens, SERMS, and aromatase inhibitors. 3, Indications for surgery: ① if the onset has been more than 18 months and the fibrous tissue is irreversible; ② long-term; ③ no pathology; ④ no signs; ⑤ non-tumor etiology; ⑥ patient’s desire.