In true precocious puberty, the secondary sexual characteristics of both boys and girls appear before the normal age of puberty (earlier than 8 years old for girls and 9 years old for boys), but the procedure is similar to that of normal development. The clinical manifestations of girls are firstly breast development, with nucleus formation and local elevation into a small mound, while the nipple and areola gradually increase in size. At the middle stage of breast development, pigmentation of the areola and nipple appears. At the same time, since the early stage of breast development, the growth rate is accelerated and the peak of growth and development is advanced, the subcutaneous fat increases significantly, and the height and weight often exceed those of children of the same age. Most of the pubic hairs appear in the year after breast development, while the axillary hairs appear even later, often after menarche. The internal and external genitalia are enlarged, the labia minora are hyperpigmented, and white vaginal discharge appears. The age of menarche is early and there may be ovulatory menstruation. The above developmental process is continuous and progressive until the final sexual maturity and fertility is achieved, but the speed of the process varies from person to person. In true precocious puberty in both sexes, the bone age is often significantly higher than the actual age, and thus the epiphysis matures too quickly and heals early, which will eventually affect the lifelong height of adults. Enlargement of testicles is the first important feature of male precocious puberty, followed by penile growth, scrotal enlargement, increased scrotal skin folds, deepening of pigmentation, growth of pubic hair, increased penile erection, seminal emission and even sperm growth. The sequence of appearance of male secondary sex characteristics such as axillary hair, beard, throat nodes, and voice change is also similar to that of normal pubescent children, except for earlier bone age. In the middle stage of testicular development, the growth rate of the child is accelerated, but the increased bone maturation also leads to premature healing of bone age. Children with true precocious puberty, both male and female, have physical and sexual characteristics similar to those of older children with normal puberty, but their intellectual development is still consistent with their actual age.