The measure of a successful guideline implementation is the ability to present data on the improved health status of the population addressed by the recommendations. Performance measures are selected based on their validation and the ability to monitor large populations at a reasonable cost. At the time of the initial National Asthma Education and Prevention Program (NAEPP) guideline in 1991,1 asthma morbidity and mortality were increasing. These trends have plateaued, and the annual mortality from asthma appears to be declining despite the increasing prevalence of the disease. Although these changes appear to be positive, cause and effect need to be demonstrated.