Undernutrition, or protein-energy malnutrition as it is often called, may occur at any stage in life. Most often, however, it is a symptom of developmental impairment that results from causes primarily operating during intrauterine life and the first three years. It kills nearly half of all children in developing countries and leaves those who sur-vive functionally disadvantaged for life. In this paper, the focus is on studies from developing countries that assess effects of childhood undernutrition on physical and cognitive development at school age, adolescence and adulthood. This is not because effects during early childhood are unimportant or unknown. Rather, it is because less is known and written about long-term consequences.