Increasing evidence suggests a developmental origin for a number of human diseases, notably after intrauterine or postnatal nutrient deprivation. Nutritional changes readily translate into alterations of somatic growth. However, whereas intrauterine growth retardation often shows postnatal catch-up growth, recovery from food restriction immediately after birth is limited. Therefore, we investigated whether early postnatal nutrition (undernutrition and overfeed-ing) modifies plasticity of growth through developmental control of the somatotropic hormone axis. We used cross-fostering in mice to induce changes in early nutrition, and examined endocrine growth regulation and the development of specific disease phenotypes in adults. We showed that underfeeding during the early postnatal period delayed growth, whereas over-feeding accelerated it. In both cases, final body size was permanently altered. We found coordinated alterations in pituitary GH, plasma IGF-I and acid labile subunit, and gene expression of hypothalamic GHRH during postnatal development. These changes were consistent with the observed phenotypes. Alterations in the somatotropic axis persisted throughout adulthood. Although limited to the early postnatal period, both underfeeding and overfeed-ing led to reduced glucose tolerance later in life. These metabolic abnormalities were in line with defective insulin secretion in restricted mice and insulin resistance in overfed mice. Moreover , both restricted and overfed mice had increased arterial blood pressure, suggestive of vascular impairment. Our findings indicate a significant link between early postnatal diet, somatotropic development, and specific late onset diseases in mice. We suggest that, together with other hormones like leptin, IGF-I may play a role in modulating hypothalamic stimulation of the developing somatotropic function. (Endocrinology 150: 314-323, 2009)