The beginning of puberty is marked by breast growth in girls and testicular enlargement in boys. These occur at the age of 10.5 ± 2.0 years in females and 11.5 ± 2.0 years in males. Recent but controversial publications suggest that these events are being observed at younger ages, at least in the USA. There are no studies demonstrating that this is true in Chile. For this reason we still consider that puberty is precocious when it occurs before 8.0 years in girls and before 9.0 years in boys. True or central precocious puberty (CPP) must be distinguished from peripheral or pseudoprecocious puberty (PPP), from premature telarche and from premature adrenarche. We suggest that the workup of a patient with premature development should include an LHRH test to demonstrate if the hypothalamic-pituitary axis is activated, plasma levels of sex steroids, bone age and pelvic ultrasound in girls. All children with CPP should have a CAT scan or MNR of the brain, since a lesion of the central nervous system is observed in 15% of the girls and 50% of the boys whith CPP. Additional studies are needed in cases of PPP. The aim of treating CPP is to avoid adult short stature that results from premature fusion of the epiphysis and to avoid eventual emotional and psychological stress. Treatment consists of monthly intramuscular injections of a depot preparation of LHRH analogs. Suppression of pituitary and gonadal activity produces regression of secondary sex characteristics and slowing down of growth velocity and bone maturation. The opportunity, duration of treatment and their effect on final stature are discussed (Rev Méd Chile 2003; 131: 95-110)