Coronary heart disease (CHD) originates early in life and numerous studies have shown inverse associations between body size at birth and CHD in adult life. Recently it has been shown that the increased risk for CHD associated with a small body size at birth is modified by growth during childhood. The greatest risk for CHD is noted in individuals with small body size at birth and who 'catch-up' in weight and body size during childhood. An increase in body weight and body mass index during the first year of life is however associated with a reduced risk of CHD. These recent findings add to the evidence that optimizing early growth is an important area in primary prevention of CHD. There are several potential mechanisms explaining the association between a non-optimal early growth and CHD. Behavioral, physiological, hormonal and genetic factors influence growth. Although socio-economic factors influence the risk of CHD, the association between slow fetal growth and CHD is not caused by confounding socio-economic factors. Biological programming - the process whereby a stimulus during critical periods of development has long lasting or lifelong effects on metabolism - is proposed to mediate the effects between early growth and adult diseases.