Asthma is a leading chronic illness among children and adolescents in the United States. This study examined the relationship between asthma and both overweight and physical activity levels. Results are based on data from the Centers for Disease Control and Prevention's 2003 national Youth Risk Behavior Survey, a cross-sectional survey of health risk behaviors among a representative sample of high school students in the United States. The overall survey response rate was 67% and the results are based on weighted data. SUDAAN was used for all data analysis (prevalence estimates and logistic regression) because it accounts for the complex sampling design of the survey. Significantly more students with current asthma than without were overweight (odds ratio [OR] = 1.4; 95% confidence interval [CI] = 1.1, 1.6) and described themselves as overweight (OR = 1.2; 95% CI = 1.0, 1.4). Significantly more students with current asthma than without used a computer for non-schoolwork 3 or more hours/day (OR = 1.3; 95% CI = 1.1, 1.5). No significant differences were found for participation in sufficient vigorous or moderate physical activity or strengthening exercises among students with and without current asthma. Unlike some other risk factors for developing or exacerbating asthma, overweight and physical activity are generally modifiable. School and community policies and programs can play an important role in asthma management, including promoting the maintenance of an appropriate weight and encouraging continued physical activity.