The prevalence of asthma is increasing in all age groups, but most particularly in children under the age of 18 years. In 1992, the prevalence of self-reported asthma among persons under 18 years of age was 7.2 percent, compared to 5.1 percent among all persons. The most rapid increase in asthma has occurred in children under 5 years old, with rates increasing over 160 percent over the past 15 years. Among all ages, over 450,000 hospitalizations, 5,000 deaths, and more than 100 million days of restricted activity are due to asthma every year. Yet the burden of asthma disproportionately affects children. For example, asthma hospitalization rates are highest among persons age 0-4 years, and have increased over 28 percent in the last 15 years; mortality rates increased faster among those aged 5 to-12 years than among those age 15-34 years and neither changes in disease coding nor improved recognition of asthma fully explain these increases. Nearly one third of children restrict their activities due to asthma, including participation in physical education and sports.