There are two processes: embryonic sexual differentiation and growth of reproductive organs, secondary sexual characteristics and reproductive functions during puberty. Embryonic sexual differentiation begins at fertilization, where the short arm of the Y chromosome determines the genetic sex of the embryo. The development of the reproductive system is regulated through the hypothalamic-pituitary gonadotropin-gonadal axis. Steroids secreted by the gonads after 26 weeks (150 days) of fetal life inhibit the secretion of luteinizing gonadotropin-releasing factor (LRF), so the gonads and sexual characteristics do not develop during prepubertal period. The endocrine changes at the beginning of puberty are initiated by the maturation of the hypothalamus, which increases the secretion of hypothalamic gonadotropin-releasing hormone and the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH) by the pituitary gland, and the gonads begin to develop and sexual characteristics begin to appear. Therefore, the reproductive system is the most delayed of all systems, growing slowly from birth until puberty, remaining in an infantile state and functioning in a resting phase. By puberty the reproductive system grows and develops rapidly, lasting about 6 to 7 years. There is great individual variation in the age of pubertal emergence and the order of appearance of secondary sexual characteristics. There is a strong correlation with the timing of gonadal development in families. In our country, precocious puberty is defined as the appearance of secondary sexual characteristics before the age of 8 for girls and 9 for boys, i.e., the early appearance of puberty. Delayed sexual development is defined as the absence of secondary sexual characteristics in girls after the age of 14 and in boys after the age of 16.