1. Background: Asthma remains a significant source of morbidity and mortality in children. In the United States, more than 11 million people reported having an asthma attack in the year 2000, and more than 5 percent of all children younger than age 18 reported having asthma attacks. The trend of increasing asthma-associated morbidity and mortality that occurred during 1980-1995 has not continued for all measures. During 1995-1998, the rate of emergency department visits for asthma increased, while the rate of hospitalization and death decreased for all age groups, except children younger than age 15. Asthma remains a significant problem despite scientific advances that generated greater understanding of the mechanisms of asthma and the development of therapeutic approaches that can reduce morbidity.