Epidemiological surveys demonstrate that rapid increase in allergic diseases is a real phenomenon. In developed countries they are about the commonest chronic diseases, reaching between 15% and 30% of the population. Adverse reaction to food can be divided into toxic reaction and non-toxic reactions. The non-toxic reactions are divided into non-immune mediated and immune mediated, these are considered food allergic reactions. We showed our experience in a 4 y survey, individualized by food allergens during the first two years of life. In Spain egg white protein is the most common allergen followed by cow's milk and peanuts. These three food items represent half of the sensitizations in children under 2 y of age. After 4 y sensitivities to vegetable allergens such as nuts, fruits and legumes are most frequent. The diagnosis of food allergy is still problematic, even in the case of atopy or IgE mediated hypersensitivity. There is a lack of standardized diagnostic procedures; the only test accepted as 'gold standard' for confirmation of food allergy and in general for food intolerance, is a properly performed double blind placebo-controlled oral food challenge. Negative results should be always followed by an open food challenge. This test should only be conducted in patients with a good medical condition and in a clinic or hospital setting, and only if trained personal and equipment for treating systemic anaphylaxis are present. Contraindications to a challenge test are limited to those situations that can be hazardous for the patient in relationship to the studied food. The treatment of food allergy and intolerance is avoiding the implicated food as long as necessary, until tolerance appears. Prevention of food allergy is the first goal of every pediatric allergologist. Controlled trials of food allergy prevention have been performed only in high allergic risk children.