Precocious puberty refers to the appearance of secondary sexual characteristics in boys before the age of 9 years and in girls before the age of 8 years. According to the pathogenesis and clinical manifestations, precocious puberty is divided into central precocious puberty (gonadotropin-releasing hormone-dependent) and peripheral precocious puberty (non-gonadotropin-releasing hormone-dependent), which used to be called true precocious puberty and pseudo-precocious puberty respectively. Central precocious puberty (CPP) has a programmed process of initiation and maturation of the hypothalamic-pituitary-gonadal axis (HPGA) similar to normal pubertal development until the maturation of the reproductive system; that is, the hypothalamus secretes and releases gonadotropin-releasing hormone (GnRH) in advance, which activates the pituitary gland to secrete gonadotropin to develop and secrete sex hormones, resulting in the development of internal and external genitalia and This results in the development of internal and external genitalia and the presentation of secondary sexual characteristics. Peripheral precocious puberty is caused by the increase of sex steroid hormones in the body to the level of puberty due to various reasons, so only the early appearance of secondary sexual characteristics, but does not have a complete sexual development process. Etiology 1. Central precocious puberty. (1) Organic lesions of central nervous system, such as hypothalamus, pituitary tumor or other central nervous system lesions. (2) Transformation from peripheral precocious puberty. (3) Idiopathic central precocious puberty (ICPP), if no organic lesion is found. (4) Incomplete central precocious puberty, a special type of CPP, refers to the early appearance of secondary sexual characteristics in the affected child, and its control mechanism also lies in the activation of the hypothalamic-pituitary-gonadal axis, but its sexual characteristics development is self-limiting; the most common type is simple premature breast development, if it occurs in girls within 2 years of age, it may be due to the hypothalamic-gonadal axis being in a physiologically active state, also known as “micropuberty”. Girls are more likely to have ICPP, accounting for more than 80%-90% of CPP; while boys are the opposite, with more than 80% being organic. 2. Peripheral precocious puberty. (1) Classification according to the characteristics of the second sex characteristics: when the early appearance of the second sex characteristics is the same as the original sex of the child, it is called homosexual precocious puberty, and when it is opposite to the original sex, it is called heterosexual precocious puberty. (2) Classification of common causes a. Girls: Homosexual precocious puberty (secondary sex characteristics of girls): seen in hereditary ovarian abnormalities such as McCune-Albright syndrome, benign ovarian occupational lesions such as autonomic ovarian cysts, estrogen-secreting adrenocortical tumors or ovarian tumors, ectopic human chorionic gonadotropin (HCG)-secreting tumors, and exogenous estrogen intake, etc. Heterosexual precocious puberty (male secondary sex characteristics): seen in congenital adrenocortical hyperplasia, androgen-secreting adrenocortical tumors or ovarian tumors, and exogenous androgen intake, etc. b. Boys (1) Homosexual precocious puberty (male secondary sexual characteristics): seen in congenital adrenocortical hyperplasia (more common), adrenocortical tumors or testicular mesenchymal cell tumors, ectopic HCG-secreting tumors, and exogenous androgen intake, etc. (2) Heterosexual precocious puberty (female secondary sexual characteristics): seen in estrogen-producing adrenocortical tumors or testicular tumors, ectopic HCG-secreting tumors, and exogenous estrogen intake, etc.