Over the last decade growing evidence has been documented on the relationship between intrauterine growth retardation (IUGR) and pubertal development indicating changes in timing and progression of puberty. These changes in pubertal development are part of a growing list of IUGR-related diseases, which includes type 2 diabetes mellitus, cardiovascular disease, short stature and polycystic ovary syndrome. The influence of IUGR on the mechanisms behind the onset of puberty is still elusive. In the absence of prospective studies on gonadotropin-releasing hormone pulse patterns in IUGR children, other markers of pubertal development such as age at menarche in girls and progression of puberty have been employed. We investigated pubertal development and DHEAS levels in children born small for gestational age (SGA) after third trimester growth retardation and children born appropriate for gestational age (AGA). A faster progression of puberty was found in girls but not in boys. DHEAS levels tended to be higher in SGA children than in AGA children. In animal studies using two rat models, growth and onset of puberty based on perinatal undernutrition were also investigated. In one model intrauterine growth retardation was induced by ligation of the uterine arteries (IUGR) at day 17 of gestation and in the other model postnatal food restriction (FR) was induced by increasing litter size after birth until weaning. In both models, the rats showed a persistent growth failure. Onset of puberty was defined by vaginal opening (VO) in female rats and by balanopreputial separation (BPS) in male rats. At onset of puberty IUGR and FR rats had a lower body weight compared to controls, indicating that no threshold for body weight is needed for the onset of puberty. In the IUGR female rats, the onset of puberty was delayed and in the FR female rats the onset of puberty was in time. In both IUGR and FR female rats VO and first cycle were uncoupled. In IUGR female rats, at VO, at first cycle and at the age of 6 months the ovaries showed a decline in number of follicles indicating that intrauterine malnutrition in the female rat has a permanent influence on the growth and development of follicles. In the FR female rats, at VO, the ovaries showed a normal number of follicles but an abnormal maturation pattern. At the time of first cycle and at the age of 6 months normalization in follicle growth pattern was observed. These findings suggest that postnatal undernutrition has a transient influence on follicle growth and development. In male rats, both models showed delayed onset of puberty and impaired testicular function, as shown by decreased testosterone levels. These data indicate that early malnutrition during different critical developmental time windows may result in different long-lasting effects on pubertal development in both humans and rats.