Clinically, it has been shown that there are many people who consider themselves to have a short penis who actually do not have a true small penis, but rather an illusion caused by individual differences and other factors. In view of this situation, the following is an introduction to the definition, examination and symptom presentation of penile shortening, as well as treatment methods. I. Penis length measurement standard: Penis length measurement refers to the retraction length, that is, the head of the penis is stretched as straight as possible by hand so that its length is equivalent to the length of a fully erect penis, and the distance from the front of the pubic symphysis to the tip of the penis head is measured with a measuring tape. The size of the penis is generally expressed by the length and circumference of the penis when it is weak and when it is erect. The average retracted length of domestic adult male is (13.3±1.6) cm, and the average length of domestic adult male penis at weakness is (7.1±1.5) cm. for normal appearance, penis length less than 2.5 standard deviations above the average of normal penis length is called small penis. The concept of real short penis: 1. Length: less than 2.5 cm when the penis is weak before puberty and less than 5 cm during puberty and adulthood. Circumference: less than 1 cm before puberty tide, less than 7.5 cm at puberty. 2.Development of secondary sexual characteristics: such as vocal cords, beard, gum hair, pubic hair, throat nucleus, etc. 3, abnormal development of organs, sexual dysfunction, no erectile function, no sperm, no fertility. With the above points to be considered a real short penis. Second, the etiology Penis development is regulated by the hormones of the pituitary-hypothalamus-gonadal axis. After 14 weeks of embryonic hormone deficiency can affect penile development. Common causes include: 1. hypogonadism with insufficient gonadotropin secretion (hypothalamus secretion abnormalities, etc.); 2. hypogonadism with excessive gonadotropin secretion (testicular secretion abnormalities: testicular agenesis or incomplete descent, etc.); 3. sex chromosome abnormalities: Klinefelter syndrome, multiple X syndrome, multiple chromosome abnormalities, etc.; 4. acquired developmental delay: such as low blood testosterone in obese children 5. Prepuce or prepuce with recurrent infection hinders normal penile development; 6. A few primary penile shortening with unknown causes. Diagnosis 1. Medical history and family history: Collect family history, mother’s pregnancy history and other relevant information; first of all, we should know in detail whether there is any history of hypospadias, cryptorchidism, small testicles and other abnormal development of organs in the family, whether there is a history of consanguineous marriage, whether there are intellectual abnormalities, whether there are abnormalities in smell, hearing, vision and so on. 2.Examination: pay attention to the presence of abnormal facial features and finger and toe deformities. Measure the length and circumference of the penis, the location, size and texture of the testicles. 3.Laboratory examination: mainly check karyotype and sex hormones (T, FSH, LH). 4.If FSH and LH are high and T is low, hCG stimulation test should be added to exclude primary low testicular function; if T, FSH and LH are low, hCG stimulation test should be done first to determine testicular function, and then gonadotropin-releasing hormone stimulation test should be done to identify anterior pituitary function. If all of these tests are normal, the cause of penile shortening should be considered to be localized in the hypothalamus. If T, FSH and LH are normal, it is important to consider whether the penile receptors are insensitive to androgens. 5.Imaging examination: Imaging examinations such as cranial CT and MRI should be done for those suspected of hypothalamic and pituitary developmental abnormalities or lesions. (1) HCG stimulation test The HCG stimulation test is used to detect the androgen secretion function of Leydig cells. Nowadays, the multiple injection method is commonly used: HCG 1 500U, intramuscularly, once every other day, for a total of 3 times. Blood specimens are taken before injection and early in the morning of the next day after 3 injections, and testosterone and DHT are measured; in patients with normal testicular function, the level of testosterone can be increased by more than 2 times; in patients with no response or low response, primary testicular insufficiency or absence of testes; in patients with secondary hypogonadism, the response depends on the degree of hypothalamic or pituitary damage; in patients with delayed somatic puberty, the response is often normal; in patients with delayed response, the blood testosterone can rise after multiple HCG injections. The blood testosterone can rise after repeated HCG excitation, which can exclude the testicular insufficiency itself. (2) GnRH stimulation test This test is used to detect the endocrine function of hypothalamus and pituitary gland, and it is not significant when performed at school age or before. The stimulant can be Gn- RH or GnRHa (GnRH mimetic). When the boy’s bone age is greater than 14 years, he is given testosterone 11 acid 40 mg/d orally for 7 d, and then the GnRH stimulation test is performed, usually at 2.5 μg/kg intravenous GnRH, and blood is collected before and 30, 60, and 90 min after the injection to detect peak LH and FSH responses. When LH<5U/L can be considered gonadotropin deficiency. Nowadays, GnRHa stimulation test is more recommended. FSH value is not significant for diagnosis, but LH< 8U/L can be diagnosed as gonadotropin deficiency. The test has 100% sensitivity and 96% specificity, and is simple and easy to perform. (3) Androgen diagnostic treatment This method is used to detect the presence or absence of androgen resistance. Testosterone propionate 25mg is injected intramuscularly once every 3 weeks or 40mg of oral androgen daily for 4 months. If the penis can be enlarged, androgen resistance can be excluded. Studies of hypothalamic-pituitary-gonadal axis function during the life span have found that the postnatal period of 6 months is another window of time to diagnose gonadotropin deficiency in boys. As fetal GnRH pulse initiation continues, FSH, LH, and testosterone secretion increases in boys after birth and decreases after 6 months. Early diagnosis provides the possibility of early treatment. Treatment 1.Psychotherapy; 2.Medication; 3.Penile lengthening.