Background : Allergy skin test is a major tool in the diagnosis of atopy. Some of the patients with respiratory allergy such as rhinitis and asthma show often no sensitization for common inhalant allergens when skin prick test is performed. Previous literature on the relationship between serum total IgE and body mass index (BMI) has been inconsistent. It is not known how this relationship is in patients with nonatopy. Objective : We sought to examine the relationship of serum total IgE and body mass index in respiratory allergy patients with nonatopy. Methods : Skin prick tests were performed with 33 common inhalant allergens on 934 respiratory allergy patients from January 2007 through December 2007 at a University hospital and total serum IgE was measured. Atopy was determined by a positive skin prick test response to at least one common inhalant allergen. Among the studied subjects, 526 patients were nonatopy. We excluded the cases with more than 500 IU/mL of total serum IgE because which levels of IgE were more associated with other causes, such as parasite infections. Results : The subjects with nonatopy and less than 500 IU/mL of total IgE level were 468 patients consisted of 169 male and 299 female. When the cutoffs were used for underweight, overweight, and obesity corresponding to BMI of 18.5, 23.0, and 25.0 kg/m2, the levels of mean total IgE in female patients were 41.1±41.0 in underweight (n=14), 64.6±87.3 in normal weight (n=104), 78.9±99.9 in overweight (n=57), and 85.5±87.6 IU/mL in obese patients (n=124), respectively. Mean total IgE levels were significant higher among obese and overweight patients than among the others (83.4 vs. 61.8 IU/mL, p=0.036). No statistical significance was observed in male patients. Conclusion : Obesity may be a contributor to the increased level of total serum IgE in female patients with nonatopic respiratory allergy diseases.