In this review I have described the pathophysiology of allergic disorders of the gastrointestinal tract. Situations where the intestine cannot be a complete barrier to foreign allergens and antigens were discussed and etiological factors of gastrointestinal allergy were detailed. Clinical features of gastrointestinal allergy include diarrhea, vomiting, abdominal pain and colic, intestinal hemorrhage and malabsorption as well as symptoms and signs outside the gastrointestinal tract such as chronic rhinitis and asthma in the respiratory system, urticaria, angioedema and eczema as dermatological signs, headache, insomnia, hyperkinesis as central nervous system manifestations, failure to thrive and anaphylaxis as constitutional reactions. Milk allergy was discussed as an example of food allergy. Immunology of the gastrointestinal tract was presented, with examples of four types of hypersensitivity reactions, and gastrointestinal disturbances of immunodeficiency disorders and syndromes were named. Lastly, the autoimmune mechanism and the gut were described, with particular discussion of ulcerative colitis as an example of an autoimmune disease.