Morbidity and mortality from pediatric asthma have been increasing in developed countries over the past three decades, making asthma the most common chronic disease of children. A joint session at the American Thoracic Society meeting in May 2000 was titled "Childhood Asthma: Is Change in Lifestyle the Key"? During this session, the hypothesis was advanced that a lack of physical exercise and higher levels of childhood obesity may be contributing to an increased incidence of asthma among United States children.