Klinefelter syndrome, also known as XXY syndrome or Klinefelter’s syndrome, is caused by an extra X chromosome in the cells of male patients; the incidence is 1 in 1000 male newborns and is the most common disorder causing male hypogonadism. Clinical features: The typical phenotype of Klinefelter syndrome is characterized by tall stature, abnormal development of secondary sexual characteristics, infertility and gynecomastia. In the neonatal period, an increase in body length is seen, and after the age of 5 years, the body growth rate begins to accelerate, and by the time of puberty, the patient shows an elongated stature, which is evident in the lower extremities. The penis and testes are relatively small at birth, and the spermatogenic tubules show glassy and fibrous degeneration at maturity, with no sperm production. The secondary sexual characteristics are abnormal, including beard, scant body hair, female-like pubic hair distribution, and inconspicuous laryngeal nodes. About half of the adolescent patients have a female-like mammary gland overdevelopment. With the exception of individual patients with 46, XY/47, XXY mosaic, all simplex Klinefelter syndrome suffer from azoospermia or oligospermia. Treatment: The main treatment is symptomatic. 1. Androgen replacement therapy: Begin at the age of 12-14 years. Start with small doses and gradually increase them according to the response to promote the development of secondary sex characteristics, psychological and behavioral development and improve osteoporosis. Androgens can improve and maintain secondary sexual characteristics, masculinize the patient’s body shape and increase sexual desire, but cannot treat the already atretic sex cells and the already enlarged breasts. 2.Surgical treatment: Correct the female physique and restore the male physique. 3. Infertility: Artificial insemination can be tried with assisted reproduction techniques, the main method being intracytoplasmic sperm injection in the oocyte. Prevention: 1. Before conception, avoid ionizing radiation, overdose and exposure to chemical substances and viral infections; pay attention to personal hygiene, maintain good living habits, and pay attention to moderate physical exercise to enhance the body’s resistance ability. 2. The disease is related to the advanced age of the mother, and prenatal diagnosis should be made for the advanced age of the mother.