Purpose: Although the cause of adenotonsillar hypertrophy (ATH) remains unknown, some studies have shown that allergy may be a risk factor. The present study was undertaken to investigate the presence of allergen specific IgE in adenotonsillar tissues and serum in children with ATH. Methods: Specific IgE levels against 21 allergens (Dermatophagoides pteronyssinus (DP), Dermatophagoides farina(DF), cockroach, cat, dog, alder, birch, oak, Japanese cedar, orchard grass, Bermuda grass, Lilium grass, mugwort, ragweed, Alternaria alternaria, Aspergillus fumigatus, egg white, cow\'s milk, Soy bean, Wheat, and Peanut) in homogenates of adenotonsillar tissues and serum of 102 children with ATH were measured using the ImmunoCAP system. Systemic atopy was defined as having a positive sIgE test to at least one of the allergens in serum, and local atopy was defined as having a positive sIgE test to at least one of the allergens in adenotonsillar tissues. Results: Fifty-five children (53.9%) were sensitized to at least one allergen in serum and 70 (68.6%) were sensitized to more than one allergen in adenotonsillar tissues. Among 55 children with positive serum sIgE expression, 53 (96.4%) exhibited positive sIgE expression in adenoid and tonsils. Of the 47 subjects negative for serum sIgE expression, local sIgE was detected in 17 (36.2%). The most prevalent locally sensitizing allergen was house dust mite (85.7%), followed by tree (70.0%), grass (54.3%), food (40.0%), weed (28.6%), mold (15.7%) and dander (14.3%). The positive rate of inhalant allergen sIgE in adenoids was significantly higher than in tonsils. However, the positive rate of food allergen sIgE in tonsils was significantly higher than in adenoids. Conclusions: The results of this study suggest the presence of a localized allergic reaction in adenotonsillar tissue even in the absence of systemic atopy in children with ATH.