The incidence of precocious puberty has increased significantly in recent years, seriously affecting the physical and mental health of children and causing anxiety among parents of affected children. Some parents ask the doctor to check the sex hormones of their children when they arrive at the hospital, while some parents refuse to perform gonadotropin-releasing hormone stimulation test for fear of drawing too much blood from their children. These practices are not scientific. How should we correctly diagnose precocious puberty? First: firstly, to determine whether the child is precocious? The Ministry of Health’s “Guidelines for the Treatment of Precocious Puberty” defines precocious puberty as the appearance of secondary sexual characteristics in boys before the age of 9 and in girls before the age of 8. In other words, girls have hard and enlarged breasts and a little pubic hair on the perineum; boys have enlarged testicles, thickened penis and pubic hair on the root of the penis. If the above situation indicates the development of secondary sexual characteristics, but clinically, we often see girls come to the hospital after the age of 8 and boys after the age of 9. At this time, in addition to the routine physical examination of the child, the doctor also needs to perform bone age and pelvic ultrasound examination to determine whether the bone age is advanced and whether the uterus, ovaries and follicles are enlarged, if the bone age is advanced and the uterus, ovaries and follicles are enlarged, the diagnosis of precocious puberty is established. Second: To determine whether it is central precocious puberty or peripheral precocious puberty? There are two types of precocious puberty, central and peripheral, and their treatment and prognosis are very different, so it is important to determine which type of precocious puberty the child has. Central precocious puberty refers to the activation of the hypothalamic-pituitary-gonadal axis and the increase of gonadotropins and sex hormones in the child’s body, resulting in the early development of sexual characteristics. Peripheral precocious puberty, on the other hand, is the appearance of secondary sexual characteristics due to the increase of gonadotropin levels in the body caused by various reasons, without any real activation of the hypothalamic-pituitary-gonadal axis. Since pituitary gonadotropins (folliculopoietin and luteinizing hormone) are secreted in a pulsatile manner, a single blood test often leads to a missed diagnosis, especially in those with stage B2 breasts, where there can be a 50% missed diagnosis, so a gonadotropin-releasing hormone stimulation test must be performed. If the breast is in stage B4 or menstruation has already started, gonadotropin-releasing hormone stimulation test is not available and a single blood test is sufficient. In addition, some children with secondary sexual characteristics appear soon, the increase in bone age is not obvious, even if it is central precocious puberty, gonadotropin-releasing hormone stimulation test, luteinizing hormone level may not be elevated, for such children may not rush to perform stimulation test, closely observe the progress of secondary sexual characteristics and bone age, and if necessary, perform gonadotropin examination. If gonadotropin-releasing hormone stimulation test is performed, the peak of luteinizing hormone is greater than 3.3-5.0 IU/L, and the ratio of luteinizing hormone to folliculopoietin is greater than 0.6, it can be diagnosed as central precocious puberty. Third: Etiological diagnosis Once the diagnosis of central precocious puberty is confirmed, it is necessary to clarify whether there are any abnormalities in the central nervous system (intracranial). Central precocious puberty can be caused by organic lesions of the central nervous system (such as intracranial tumors) or transformed from peripheral precocious puberty, or no organic lesions of the central nervous system are found. The majority of girls with central precocious puberty (69%-98%) have no organic lesions in the central nervous system, while 60-80% of boys with central precocious puberty have intracranial organic lesions. Therefore, it is advisable to perform MRI of the head in children with central precocious puberty, especially in 1) all boys diagnosed with central precocious puberty, 2) girls with onset before 6 years of age, and 3) those with rapid sexual maturation or other manifestations of central pathology. The diagnosis of the etiology of peripheral precocious puberty is more complex and further endocrine examinations are performed according to specific clinical features and after the initial screening of endocrine hormones, and impactological examinations of the gonads, adrenal glands or other related organs are performed as needed.