The literature on the long-term effects of nutritional deficiencies in early life is reviewed. The severity and duration of the deficiency, the stage of the children's development, the biological condition of the children and the socio-cultural context may all modify the effect. There is substantial evidence that reduced breast-feeding, small-for-gestational-age birth weight, Fe and I deficiency, and protein-energy malnutrition (PEM) are associated with long-term deficits in cognition and school achievement. However, all these conditions are associated with poverty and poor health, which may account for the association. It is difficult to establish that the long-term relationship is causal, as it requires a randomized treatment trial with long-term follow-up. Such studies are only available for I deficiency in utero and early childhood PEM. Results from these studies indicate that I deficiency has a long-term effect and PEM probably has a long-term effect.