Gastro-intestinal disorders were described during long lasting exercise. However, no systematic evaluation was done before the study of the French Medical Society of Triathlon, which realized an epidemiologic analysis during the French triathlon championship in 1989. The aims of this study were to evaluate the prevalence and the nature of different gastro-intestinal symptoms, to precise the severity and the consequences of these disorders, and to evaluate the self-medication. This study concern 25,640 competitors of the 101 meetings of the French triathlon championship 1989 (75 category A, 19 category B and 7 category C). Two thousand two hundred and seventy four competitors had gastric symptoms like nausea, epigastgric pain or vomiting (8.9%); 2,046 competitors had intestinal troubles like diarrhea or abdominal pain (8%). These results confirm the suffering of the gastro-intestinal tract during a long lasting exercise like a triathlon. These disorders are well known, so self-medication was used for gastric symptoms (0.7%) or intestinal disturbances (18.2%).