Intra-uterine life has been identified as a possible critical period for the development of obesity risk in both adults and children; others have highlighted the importance of growth and nutrition in the first few years. It is suggested that fetal growth, as assessed by birth weight, may programme lean body mass later in life. Children who are born small for gestational age also have a predisposition to accumulating fat mass, particularly intra-abdominal fat. It is not yet clear whether this predisposition is due to their prenatal growth restraint, their rapid postnatal catch-up growth or a combination of both. Recently, genetic and heritable factors have been shown to contribute to both rapid postnatal growth and childhood obesity risk in children and adults. Future studies should explore their timing of action and potential interactions with markers of antenatal growth restraint.