Identification of the characteristics that make certain travelers more likely to develop diarrhea, the most common illness affecting international travelers, can lead to prevention of the illness and to improved understanding of endemic diarrheal disease in developing countries. Travelers' diarrhea, a syndrome with a spectrum of clinical symptoms, is most frequently characterized by watery diarrhea, cramps, and nausea. The highest attack rates have been reported in travelers from the United States or northern Europe to less-developed, particularly tropical, countries. Among travelers from less-developed countries, diarrhea has been correlated with higher socioeconomic status. The findings that country of origin and socioeconomic status may affect the frequency of previous exposures to enteric pathogens suggest that persons with prolonged exposure acquire immunity and are at lower risk of developing travelers' diarrhea. Although few studies have shown a clear correlation between the eating of specific foods and the development of travelers' diarrhea, the syndrome has been associated with eating in public places.