To assess the incidence rate and the characteristics of traveler's diarrhea in small children ages 0 to 2 years, children ages 3 to 14 years, and adolescents ages 15 to 20 years a retrospective survey was conducted. Of the pretravel visitors to the Zurich University Vaccination Center, all those ages 0 to 20 years were selected between October, 1987, and May, 1988. They received a questionnaire within 2 weeks after returning home. Of the 446 young travelers who were recruited, 363 (81.3%) could be evaluated. Within 14 days in the tropics or subtropics, traveler's diarrhea occurred in 8 of 20 (40.0%) small children, in 4 of 47 (8.5%) children ages 3 to 6 years, in 10 of 46 (21.7%) children ages 7 to 14 years and in 90 of 250 (36.0%) adolescents (P = 0.0003). In small children the clinical course tended to be severe and prolonged (average duration, 29.5; median, 17.5 days) when compared with other age groups (3 to 5 days). In 40% of all the children the parents reported that they had consistently practiced dietary preventive measures. For self-treatment oral rehydration solutions were used in 5.0% and loperamide in 33.8%. In conclusion adults should be discouraged from taking small children to developing countries unless necessary. Parents should be instructed about how to prevent traveler's diarrhea and about the mainstay of self-therapy in pediatric patients by oral rehydration solutions.