Atopy is associated with the presence of IgE towards common harmless antigens. However, presence of IgE, also called sensitization (elevated specific serum IgE and/or positive skin prick test) is not necessarily associated with clinical disease. It is estimated that more than 50% of the patients has sensitization without clinical relevance. The extent of sensitization seems only partly associated with the severity of the symptoms. So far, there are no patient determinants that can predict which of the sensitized children will respond to the offending food. For a good diagnosis of food allergy, several aspect need to be taken into account. First of all, it is important to take a thorough history of the patient, with respect to food intake and symptoms. However, in part of the patients, and especially in children, the clinical history is often unreliable. Then, sensitization is determined. Serum IgE towards the specific food is measured by CAP, and skin prick tests (SPT) can be performed using allergen extracts. However, the sensitivity and specificity of these tests are often low. Therefore, the diagnosis of food allergy is most reliable when measurement of sensitization is followed by a double-blind placebo-controlled food challenge (DBPCFC) as the gold standard to prove clinical relevance. This is an elaborate and expensive test, which is only available in specialized centers. Therefore, currently the diagnosis of food allergy is frequently based on patient history and sensitization alone, which has important therapeutic consequences. Extensive elimination diets are prescribed to these patients. The major disadvantages of extensive diets are that they can lead to psychosocial burden, eating disorders, deficiencies and growth retardation.