Although some pediatricians may trivialize allergic illnesses as just allergy, most clinicians now realize the significant impact that allergic diseases have on children9s health and quality of life. Allergic diseases, including asthma, are among the major causes of chronic illnesses in the United States, affecting approximately 50 million patients or as many as one in five children. The economic impact is enormous; asthma alone is estimated to cost more than 6.2 billion dollars of health care expenditures annually. Of all the chronic illnesses, allergic respiratory problems, including allergic asthma, is the most common cause of school absenteeism. Even though allergic disease usually is not fatal, death can result as a consequence of allergic anaphylaxis related to medication, food, or insect venom allergy or from a complication of asthma. Therefore, the pediatrician must be capable of diagnosing allergic disease so as to institute appropriate management. This review will emphasize those clinical diagnostic features ascertained by history and physical examination as well as the appropriate laboratory studies useful in the diagnosis of respiratory (inhalant) and gastrointestinal (food) allergy. General Features of Allergic Diseases Allergic diseases are immunoglobulin E (IgE)-mediated immunologic illnesses that can affect any of the body9s major organ systems either individually or collectively.