This is a review of studies on the relationship between mental development and severe malnutrition. School-age children who suffered from early childhood malnutrition have generally been found to have poorer IQ levels, cognitive function, school achievement and greater behavioral problems than matched controls and, to a lesser extent, siblings. The disadvantages last at least until adolescence. There is no consistent evidence of a specific cognitive deficit. The evidence of a causal relationship is strong but not unequivocal because of difficulties in interpreting retrospective case control studies. Marked improvements in development can occur after adoption or intervention. Therefore, the outcome depends to a large extent on the quality of the subsequent environment. It is likely that extremely deprived environments would exacerbate the effects. There is limited evidence that other nutritional deficiencies may interact with previous malnutrition in affecting cognition. The mechanism linking malnutrition to poor development is still not established.