Developmental changes during puberty in girls occur over a period of 3 - 5 years, usually between 9 and 14 years of age. They include the occurrence of secondary sex characteristics beginning with breast development, the adolescent growth spurt, the onset of menarche -  which does not correspond to the end of puberty -  and the acquisition of fertility, as well as profound psychological modifications. These events are consecutive to the stimulation of the hypothalamic- pituitary-ovarian axis, which leads to sex-steroid secretions acting on specific receptors.

Even though the reactivation of the LHRH pulse generator, already functional since the perinatal period, has been thought for 20 years to be the primum movens of puberty, the inhibitory and stimulatory neuromediators controlling this reactivation remain to be fully elucidated. Since puberty is a long, ongoing developmental process with significant individual and population differences in timing, the definition of delayed puberty for a given individual needs to be based on simple though arbitrary criteria from epidemiological data.

Although several genes involved in the hypothalamic-pituitary-gonadal maturation cascade have been characterized recently from familial or sporadic cases of primitive isolated hypogonadotropic hypogonadism (IHH), many genes influencing puberty onset remain undetermined. Identification of the Ob gene product and the role of leptin in reproduction have highlighted the influence of nutritional factors, as illustrated by the frequent association of delayed puberty with systemic diseases and/or with a negative energetic balance.

In cases of delayed puberty and/or primary amenorrhea, a complete clinical exam including a detailed history evaluates the development of secondary sex characteristics and looks for an association with growth delay and other specific features to determine etiology. This clinical check-up, which may be completed by biological, radiological and genetic investigations, will try to distinguish which girls will have permanent sexual infantilism of gonadal, pituitary or hypothalamic origin, which will undergo spontaneous but delayed puberty, and which have primary amenorrhea with developed secondary sex characteristics. Management will have to integrate etiological factors, statural prognosis, bone mass preservation and psychological factors.