Exercise-induced bronchospasm (EIB) is common in young asthmatics and obesity is becoming an epidemic in this population. Both conditions can give rise to or worsen respiratory symptoms upon exercise and may interfere with recreational and sports activities. To investigate the association between obesity and the risk and severity of EIB in asthmatic children and adolescents. This study included data from asthmatic patients aged between 7 and 19 years undergoing treadmill running tests to evaluate EIB, defined as a reduction greater than or equal to 10% in forced expiratory volume in the first second (FEV1 ) compared to baseline. Eutrophic, obese, and overweight individuals were categorized according to body mass index z-score (eutrophic, -0.5 < z ≤ 1; overweight, 1 < z < 2; and obese, z ≥ 2). Of the 156 individuals studied (42% female), 58% were eutrophic, 22% overweight, and 19% obese. Seventy-three individuals (47%) presented with EIB, with higher risk among obese (OR, 2.86; 95% CI, 1.00-8.14; P = .05). Asthma severity was another independent risk factor for EIB (OR, 2.95; 95% CI, 1.36-6.42; P = .006). The number of patients in whom FEV1 returned to baseline values (difference less than 10% from baseline) at the 13th minute after challenge was lower in obese individuals compared to eutrophic and overweight ones (P = .04). Baseline FEV1 , gender, or age were not found to be risk factors for EIB in any of the groups. Obese youngsters with asthma present a greater risk for EIB with slower recovery than their nonobese peers. Clinicians should be aware of this association, especially in those with more severe disease, for adequate recognition and treatment.