The association between increased tissue eosinophilia and allergic disease is particularly striking in the case of the gastrointestinal tract. About 80% of individuals with eosinophilic gastrointestinal disorders (EGIDs) are atopic, while half of the patients with gastrointestinal allergy show tissue eosinophilia. The function of eosinophils in gastrointestinal allergic disorders is unclear; however, a proinflammatory action is most likely. Cytokines (interleukins 5 and 3, granulocyte-monocyte colony-stimulating factor) and chemokines (eotaxin, RANTES, etc.) released by Th2 lymphocytes, mast cells and other tissue cells have been identified as major regulators of eosinophil chemotaxis and activation, but a convincing mechanism by which eosinophils are activated in an allergen-dependent manner is still lacking. The diagnostic approach comprises both histological and laboratory methods to assess eosinophilia and eosinophil activation, as well as tools to assess the allergic disease while excluding other gastrointestinal diseases such as food intolerances, infections and tumours. Treatment of allergic EGIDs includes elimination or elemental diets and drug therapy using classical anti-allergic agents such as topical corticosteroids and new approaches such as LTD4 receptor antagonists or antibodies against IL-5 or eotaxin.