The role of allergic reactions in the pathogenesis of inflammatory bowel disease and irritable bowel syndrome has been disputed. This study aimed to determine the prevalence of adverse reactions to food in patients with gastrointestinal disease. A total of 375 adult patients of a gastroenterologic outpatient clinic were examined by history, skin tests, measurements of laboratory parameters, and intestinal provocation with food allergens by colonoscopy. Some 32% complained of adverse reactions to food as a cause of their abdominal symptoms. In 14.4%, the diagnosis of intestinal food allergy could be suspected according to several criteria such as elevated total IgE, specific IgE against food antigens, eosinophilia, responsiveness to cromoglycate, and clinical signs of atopic disease. In 3.2%, the diagnosis could be confirmed by endoscopic allergen provocation and/or elimination diet and rechallenge. In conclusion, the data suggest that allergic reactions to food antigens may be a causative factor in a subgroup of patients with inflammatory and functional gastrointestinal disease.