Background. To explore the association between obesity and asthma in US children and adolescents with adjustment of other structural and behavioral factors. Method. Prevalence and associated risk factors of asthma were explored in 102,273 children and adolescents in the National Survey of Children's Health (2003-2004). Subgroup analysis was performed for subjects of 0-6 year-old, 7-12 year-old, and 13-17 year-old. Crude and adjusted odds ratios for the potential risk factors were examined in univariate and multivariate logistic regressions. Results. The overall prevalence of obesity was 24.5% and that of asthma was 12.5%. The adjusted odds ratio of asthma with obesity remains significantly bigger than 1 for children in the 7-12 and the 13-17 year-old age-groups. Gender and race were significantly associated with asthma in all age groups. The two parent family structure showed significant protectiveness against asthma with children in the 0-6 year-old age group. Poverty was positively associated with asthma in the 7-12 years old age group. Having a smoker in the household increased the odds of asthma by 29% and 23.5% in the 0-6 and 13-17 year-old age-groups, respectively. Higher education level of the parents and access to healthcare showed positive association with asthma in the 13-17 year-old age group. Conclusion. Gender and race were significantly associated with asthma. In the 13-17 year-old age-groups, obesity, household education level, healthcare coverage, and household smoking were positively associated with asthma. Further studies should characterize how the family structure and household education level influence childhood asthma in 0-6 and 13-17 year-old age-groups respectively. © 2009 Informa Healthcare USA, Inc.