Rationale: Whether allergic airway inflammation mediates the association between overweight or obesity and childhood asthma is unknown.Objectives: To examine adiposity, asthma, and fractional exhaled nitric oxide (FE NO ) in U.S. children.Methods: Cross-sectional study of indicators of adiposity or obesity, FE NO (a biomarker of eosinophilic airway inflammation), and asthma in 2,681 children aged 6-17 years in the 2007-2010 National Health and Nutrition Examination Survey. Adiposity measures included body mass index (BMI), percent body fat (PBF), and waist circumference (WC).Measurements and Main Results: BMI, PBF, and WC were associated with asthma among children with low FE NO (odds ratio, 1.54-1.68; P , 0.01), but not among children with increased FE NO . Among children without asthma, BMI, PBF, and WC were associated with higher FEV 1 and FVC, and lower FEV 1 /FVC. Among children with asthma and a high FE NO , all adiposity indicators were associated with decreased FEV 1 /FVC (b = 21.5% to 21.7% per z score) but not with FEV 1 or FVC. Higher BMI or PBF was associated with worse asthma severity or control in children with asthma and increased FE NO , but not in children with asthma and low FE NO . Similar results were obtained in a secondary multivariate analysis of overweight or obesity (defined as BMI >85th percentile) and asthma or indicators of asthma severity or control, stratified by FE NO level.Conclusions: Adiposity indicators are associated with asthma in children with low FE NO . Among children with asthma, adiposity indicators are associated with worse asthma severity or control in those with high FE NO .