To determine if obesity is more prevalent in adolescents with asthma compared with nonasthmatic adolescents and to determine if obesity is associated with more severe asthma, we studied 265 adolescent asthmatics 12-21 years of age and 482 nonasthmatic adolescents. The prevalence of obesity in the asthmatic group was 20% compared to 17% in the control group. The prevalence of being at risk of overweight was similar for asthmatics (16%) and controls (15%). The prevalence of obesity in moderate to severe asthmatics (21%) was not different from prevalence of obesity in mild asthmatics (19%) or controls (17%). In this study of primarily African-American urban adolescents, obesity was not associated with asthma or more severe asthma.