In humans, foetal and early postnatal growth failure may have persistent consequences for growth and pubertal development in later life. During this period, the developing organs are still plastic to change their function, which may have long-lasting effects. At the time of onset of puberty, acute factors may also interfere with pubertal development. Malnutrition, as seen in anorexic patients, and chronic diseases with malabsorption or diseases with systemic effects result in a delayed onset of puberty. We have observed an earlier onset of puberty in girls with low birth weight; menarcheal age also tended to be earlier. In boys, a low birth weight tended to be associated with a later development. Two rat models with growth failure based on perinatal malnutrition have been examined, one with intrauterine growth retardation (IUGR) by ligation of the uterine arteries and one with postnatal food restriction (FR) by increasing the litter size postnatally. In both models, the rats had a persistent postnatal growth failure. The onset of puberty in female rats, defined by vaginal opening, was delayed only in the IUGR group. Despite a significantly lower weight, there was no difference in the timing of puberty onset in the FR group. In IUGR rats, the ovaries had fewer follicles, while FR rats had a normal number of follicles but an abnormal maturation pattern. In male rats, both models showed a delayed onset of puberty, defined by the balano-preputial separation, as well as impaired testicular function, shown by decreased testosterone levels. These data indicate that early malnutrition during a critical developmental time window may have long-lasting effects on pubertal development, including gonadal maturation in both humans and rats.