Acute diarrhoea, non-antibiotic associated, is a common problem and a significant cause of morbidity and mortality in old age. In most cases diarrhoea has an infectious etiology. A number of different micro organisms can cause infectious diarrhoea. Most frequent are viral infections with a benign evolution. Rehydration is the only important therapeutic measure. Infections with bacteria are less common, antibiotics should be prescribed only in severe cases, and when there is suspicion of invasive infections by enteropathogenic bacteria.