Whilst growth and its derangement in disease have been a long-standing focus in pediatrics, increasing evidence points to a further, fundamental role of early growth in the programming of later health. In studies on animals and humans, rapid early growth is associated with higher risk of obesity and cardiovascular disease, and in animals, senescence and life span - a concept encapsulated in the postnatal growth acceleration hypothesis. This hypothesis explains the benefits of breastfeeding to infants for reduced cardiovascular disease risk in terms of their slower early growth and the fetal origins hypothesis in terms of the adverse postnatal catch-up growth in infants born small. Early growth, notably prior to full term, also influences brain development and cognition - and emerging evidence suggests diverse, broader effects, for instance cancer and the onset of puberty. Understanding the mechanisms, triggers and windows for such effects is important, given the major public health implications, including potential new opportunities for primary prevention of adult disease.