Anaphylaxis is a severe allergic reaction that can rapidly progress and occasionally be fatal. In instances in which the triggering allergen is not obvious, establishing the cause of anaphylaxis is pivotal to long-term management. Assigning cause is limited, however, by the number of known exposures associated with anaphylaxis. Therefore identification of novel causative agents can provide an important step forward in facilitating new, allergen-specific approaches to management. In contrast to the view that carbohydrate-directed IgE has minimal, if any, clinical significance, recent data suggest that IgE antibodies to carbohydrate epitopes can be an important factor in anaphylaxis that might otherwise appear to be idiopathic. Here we review the evidence relating to carbohydrates in food allergy and anaphylaxis and discuss the implications of a new mammalian cross-reactive carbohydrate determinant.