The oral allergy syndrome (OAS) is a common adverse reaction to the ingestion of certain "trigger" foods and is especially prevalent in atopic individuals. Although rarely dangerous, the symptoms may concern patients. Severe forms of OAS may resemble or precede food-induced anaphylaxis. Thus, detection and recognition of OAS are important. New insights into the molecular mechanisms underlying OAS have elucidated earlier epidemiological observations that sensitivity to certain foods is related to reactivity to certain aeroallergens. This article reviews the clinical presentation, pathogenesis, and treatment of OAS.