RATIONALE: Obesity is associated with increased asthma morbidity, lower drug responsiveness to inhaled corticosteroids, and worse asthma control. However, most prior investigations on obesity and asthma control have not focused on pediatric populations, considered environmental exposures, or included minority children. OBJECTIVE: To examine the association between body mass index (BMI) categories and asthma control among boys and girls; and whether these associations are modified by age and race/ethnicity. METHODS: Children and adolescents ages 8 to 19 years (n=2,174) with asthma were recruited from the Genes-environments & Admixture in Latino Asthmatics (GALA II) Study and the Study of African Americans, Asthma, Genes, & Environments (SAGE II). Ordinal logistic regression was used to estimate odds ratios (OR) and their confidence intervals (95% CI) for worse asthma control. MEASUREMENTS AND MAIN RESULTS: In adjusted analyses, boys who were obese had a 33% greater chance of having worse asthma control than their normal weight counterparts (OR: 1.33; 1.04-1.71). However, for girls, this association varied with race/ethnicity (p-interaction=0.008). When compared to their normal weight counterparts, obese African American girls (OR:0.65; 95%CI:0.41-1.05) were more likely to have better controlled asthma while Mexican American girls had a 1.91 (95%CI:1.12-3.28) greater odds of worse asthma control. CONCLUSIONS: Worse asthma control is uniformly associated with increased BMI in boys. Among girls, the direction of this association varied with race/ethnicity.