Among the increasingly unacceptable costs of the diseases of poverty are the largely unmeasured but potentially huge human and economic long-term costs of common tropical infectious diseases, especially those such as repeated dehydrating and malnourishing diarrheal diseases (and enteric infections, even without overt liquid stools) that are so prevalent in the developmentally critical first year or two of early childhood. We review here the high costs of diseases of poverty, increasing diarrhea morbidity (despite decreasing mortality), and new emerging evidence for long-term consequences of early childhood diarrhea on growth and on physical and cognitive development, effects that may translate into costly impairment of human potential and productivity.