Dietary habits, nutrition knowledge, and gastrointestinal complaints were evaluated in 21 female and 50 male triathletes; 30 completed hemoccult slides to determine the frequency of gastrointestinal bleeding. Triathletes trained 11 h/wk with weekly distances of 5.3, 116.5, and 40.9 km for swimming, biking, and running, respectively. Mean daily energy intake averaged 9058 and 11,591 kJ for women and men, respectively; 53.8% of the energy was from carbohydrates. Mean intakes of vitamins and most minerals exceeded the Recommended Dietary Allowances (RDAs), but many had intakes below RDAs for some nutrients; greater than 60% had low zinc and copper intakes. Because 39% took a daily multivitamin-mineral supplement, some had intakes 200-600% above the RDA. Although there were notable misconceptions about nutrition, nutrition knowledge was high. Upper-gastrointestinal complaints, reported by 50%, included bloating and abdominal gas; the incidence of positive hemoccult slides was 27%. The relation among performance, dietary patterns, nutrition knowledge, and gastrointestinal function remains to be established.