A retrospective survey, which is based on interviews conducted between 1975 and 1984 with 20,000 European tourists returning from 15 destinations m various climatic zones, demonstrates that travelers' diarrhea is the most frequent health problem encountered by travelers in the tropics. The incidence varied from 4% to 51%, depending on the destination. High-risk groups were persons younger than 30 years, adventurous travelers, and travelers with preexisting gastrointestinal illnesses. Illness acquired at various geographic regions showed only minor differences in chronology and symptomatology. The clinical course of travelers' diarrhea was usually short and mild. Additionally: by longitudinal and retrospective analyses, the incidence and prognosis of gastrointestinal infections of greater severity that were acquired after a short stay in a developing country, such as giardiasis, amebiasis, typhoid fever, and cholera, were evaluated; typhoid fever and cholera, in particular, were found to be quite rare.