PROJECT SUMMARY More than 300,000 infants are born prematurely in the U.S. each year, and of these, approximately 50,000 develop chronic respiratory disease due to their prematurity. The most common respiratory manifestation is bronchopulmonary dysplasia (BPD), which affects alveolar, airway, and pulmonary vascular development. Limited data suggests that a substantial percentage of children with BPD will have long-term respiratory symptoms persisting into adult life with altered lung function trajectories. However, predicting the course of respiratory disease in children with BPD throughout the lifespan is currently difficult, compounded by the wide variation in outpatient management after initial hospital discharge. One of the most common types of medical management are diuretics. Theoretically, diuretics reduce interstitial fluid within the lungs, thus decreasing work of breathing. However, there is conflicting evidence regarding the benefits/risks of diuretic use within the neonatal intensive care unit, and virtually no data or guidelines for the use of these medications outside of the hospital. In light of the ongoing controversy that broad use of long-term diuretics in preterm infants may or may not be beneficial in the inpatient setting, our goal is to use “real-world” data to assess whether the outpatient use of diuretics reduce acute and chronic respiratory morbidities in preterm infants and young children less than 2 years of age and whether they are associated with the side effect of impaired growth. In Aim 1, we hypothesize that the use of diuretics during the first 2 years of life will result in less acute care use (e.g., emergency department visits and hospital readmissions) and decreased chronic respiratory symptoms (e.g., activity limitations and difficulty breathing). In Aim 2, we hypothesize that the use of diuretics during the first year after initial NICU discharge will result in impairment of growth. These studies will help direct our understanding and guidance for the use of outpatient diuretic use in children with BPD.