Cystic fibrosis (CF) is the most common life-threatening genetic disorder with an incidence of approximately 1:3400 in Caucasians. Although CF begins in early infancy, delayed diagnosis is common and often leads to severe, potentially irreversible malnutrition. Obstructive lung disease with recurrent respiratory infections is also inevitable;about 80 percent die from cardio respiratory failure and one-third die before age 20 years. The overall objective of this application is to quantify the associations between malnutrition and lung disease in CF by utilizing epidemiological studies in order to improve screening and treatment of CF. Specific aims are: 1) to test the hypothesis that malnutrition worsens lung disease, by developing risk models predictive of malnutrition and lung disease associations through the use of two ongoing, complimentary databases collected since 1985, namely, the CF Foundation Patient Registry and the Wisconsin Randomized Controlled Trial (RCT) of CF Neonatal Screening, and 2) to test the hypothesis that implementing a routine statewide neonatal screening program will provide similar medical benefits previously proven in RCT, by comparing the nutritional and pulmonary status of the cohort of children diagnosed through the Wisconsin Statewide Routine Cystic Fibrosis Newborn Screening Program since its inception in 1994 to the Wisconsin RCT cohort. No other investigation has comparable researchers and tools to conduct the proposed work. With a K01 award, the principal investigator has developed into a nationally recognized CF epidemiologist, with special expertise in both nutritional and pulmonary aspects. Her work related to Specifc Aim 1 has already led to changes in the clinical practices of CF. In view of the CDC's new 2004 report that recommends nationwide implementation of CF newborn screening programs with follow-up outcome studies to evaluate program effectiveness, the clinical impact as a result of completing Specific Aim 2 is also foreseeable in the near future. Accomplishing the specific aims of this grant will advance our understanding of the impact of malnutrition on lung disease progression iri CF, change the clinical practices of CF, improve the health outcomes of CF patients, and resolve the controversy on the benefits of implementing routine CF neonatal screening program for public health policy makers.