Rates of adherence to treatment for children with chronic illnesses range from 10-83%, with a majority of studies reporting that only 50% of children adhere to their prescribed treatment regimen. Adherence is poor in pediatric pulmonary diseases, such as cystic fibrosis (CF) and asthma, because of the intensity and complexity of prescribed treatments. The consequences of poor adherence are serious, leading to increased emergency room visits, more frequent hospitalizations, declines in pulmonary functioning, and shorter life span. In order to effective address these problems, it is critical to adequately measure rates of adherence, as well as the key barriers to good disease management. Although a few anecdotal reports have described possible reasons for poor adherence, there are no comprehensive studies identifying the key barriers to adherence for children with CF or asthma. Previous research indicates that many factors may be implicated, including course and type of illness, patient-provider miscommunication and regimen characteristics. The primary goal of the current proposal is to assess the extent of adherence problems in children with CF and asthma, systematically compare patterns of adherence in these two pediatric pulmonary populations, and identify the key barriers associated with poor adherence. Identification of these barriers will be directly applicable to the development of effective interventions.