Travelers to developing countries participated in a follow-up study of the health risks associated with short (less than three months) visits to these nations. Travelers to the Greek or Canary Islands served as a control cohort. Participants completed a questionnaire to elicit information regarding pretravel vaccinations, malaria prophylaxis, and health problems during and after their journey. Relevant infections were confirmed by the respondent's personal physician. The questionnaire was completed by 10,524 travelers; the answer rate was 73.8%. After a visit to developing countries, 15% of the travelers reported health problems, 8% consulted a doctor, and 3% were unable to work for an average of 15 days. The incidence of infection per month abroad was as follows: giardiasis, 7/1,000; amebiasis, 4/1,000; hepatitis, 4/1,000; gonorrhea, 3/1,000; and malaria, helminthiases, or syphilis, less than 1/1,000. There were no cases of typhoid fever or cholera.