Asthma is the most common chronic disease among children, affecting 8% to 12% or 6.1 to 8.9 million children in the United States1 and worldwide.2 Despite the high prevalence of asthma, both preventive treatment with controller medications and acute treatment of exacerbations with rescue medications including bronchodilators or oral corticosteroids are effective.3 Consensus guidelines for disease management exist4 and disease outcomes are measurable. These characteristics make asthma an ideal sentinel condition for monitoring the effects of cost-sharing on the use of prescription drugs as well as other medical services.