Diarrhea is a common problem among the elderly that can have catastrophic results. Atherosclerosis predisposes older adults to morbid sequelae from dehydration resulting from diarrhea. Deaths related to diarrheal illnesses are recognized among older adults living in the community as well as among those confined to nursing homes. Outbreaks have most often been associated with excess deaths from diarrhea among nursing-home patients. Although most cases of dehydration from diarrhea result from gastrointestinal infections, noninfectious causes of diarrhea related to prescription of laxatives, side effects of medications, and use of enteral feedings are common. Clostridium difficile infection is particularly common among older adults in hospitals and nursing homes, and relapsing disease in these groups may be more frequent than among younger adults. The approach to an elderly patient with diarrhea is to ensure proper hydration using available oral rehydration solutions, proceed with diagnostic tests likely to yield a positive result, avoid the use of harmful antiperistaltic drugs, and provide adequate follow-up of the nutritional state.