True precocious puberty is the progressive development of the hypothalamic-pituitary-gonadal axis until fertility is achieved. In addition to gender-appropriate secondary sexual characteristics, true precocious puberty is characterized by accelerated growth, early bone age and fertility. In girls, premature breast development, pubic and axillary hair development, and menstruation are the main manifestations. In boys, in addition to the appearance of pubic hair and early vocalization, testicular and penile enlargement, premature penile erection and seminal emission are also manifested. In terms of physical development, the growth spurt of height and weight is also early, so children with precocious puberty are often taller than their peers. However, early development and early skeletal maturation can lead to premature closure of the skeleton, and eventually the cessation of the growth period is usually early, so children with precocious puberty tend to end up shorter, but their intelligence is not affected, and their reproductive function in adulthood is not affected. The causes of true precocious puberty are complex, and the common true precocious puberty includes idiopathic precocious puberty or somatic precocious puberty, which accounts for about 80% to 90% of all cases of precocious puberty, especially in girls. 15% to 20% of cases occur before the age of 2.5 years when sexual characteristics appear, with a family tendency, and the development sequence is similar to normal puberty, but earlier and faster. There are also neurological diseases that cause precocious puberty, such as pineal tumor, mesencephalic malformation tumor, neurofibroma, craniopharyngioma or other tumors and other brain lesions, as well as encephalitis and traumatic brain injury, which can lead to precocious puberty. This kind of precocious puberty is often the first symptom, and only at a certain stage do the signs and symptoms of central occupancy appear, so we should be alert. In addition to dwarfism, mental retardation, and mucinous gender edema, some children with primary hypothyroidism also have early onset of secondary sexual characteristics, as evidenced by breast development in girls and testicular enlargement in boys, but still slow growth and delayed bone age. Precocious puberty will gradually disappear after thyroid hormone supplementation in these patients. Special reminder: There are also true precocious puberty that can be caused by gonadotropin and sex hormone medication.