Bone mineralization increases with age, height and weight through childhood, with a significant gain during pubertal development. Approximately 37% of bone mass is accumulated between pubertal stages 2-5. The factors driving the pubertal increase of bone mass is not fully known, but a crucial role is played by the sex steroids. Patients with central precocious puberty show an increased bone mineral density (BMD) for their chronological age, but appropriate for their bone age and pubertal stage. In girls and boys with hypogonadism, as well as in constitutional delay of puberty, the 'tempo' of puberty seems to be another important determinant of peak bone mass. Hypogonadal patients increase their BMD when treated in adulthood with sex steroid substitutive therapy, but normal adult BMD values are not reached. If these patients start sex steroid therapy at the appropriate age for the onset of pubertal development, however, a greater increase in BMD occurs. Both oestrogen and androgen receptors have been demonstrated in bone cells. Patients with oestrogen resistance or aromatase deficiency had a severely undermineralized skeleton. Reduced area and volume BMD are also present in patients with complete androgen resistant syndrome compared to normal. The pubertal increase of BMD may be the result of the coordinated activation of oestrogen and androgen receptors at the bone level in both sexes. In conclusion, the gonadal secretion of sex steroids, the tempo of puberty, and the normal function of both oestrogen and androgen receptors seem to be important factors in the acquisition of bone mass.