In most cases, protracted diarrhea in infants is due to lack of human breast milk, and iatrogenic malnutrition. Damage to the mucosa of the small intestine maintained by cow's milk proteins and malnutrition constitute main parts of a vicious circle interrupted by completely parenteral nutrition for some time, and slow reintroduction of human breast milk. This kind of therapy reduced mortality significantly. The best prophylaxis is the full support of breast feeding. As differential diagnosis the familial lethal diarrhea of the breast fed infant has to be considered. Furthermore, in case of diarrhea lasting for longer than two weeks, other less frequent causes have to be thought of, as pointed out briefly.