Occurrence of any pubertal sign before eight years of age defines premature sexual development but does not always mean precocious puberty (PP); one should distinguish borderline physiological situations which need only a follow-up and frankly pathological situations which need very precise investigations and suitable treatment. The first situations are premature thelarche, pubarche and menarche in which the height and bone maturation, pelvic ultrasonography (US) are normal for age, avoiding hormonal investigations. Conversely in the second situation, the bone age is more advanced than the height age and the pelvic US displays ovarian activity and uterine development. The next step is the characterization of the level of the mechanism of puberty: hypothalamohypophysal or ovarian: in the first case gonadotropin levels are elevated after GnRH infusion, in the second case, depressed. The aetiological diagnosis are in true PP: brain tumors malformations or hamartoma even if negative idiopathic. At ovarian level: ovarian tumors or McCune Albright syndrome or recurrent cysts. The first etiology leads to use GnRH analog in the second the treatment is more delicate.