Introduction: Bronchopulmonary dysplasia (BPD) is a major cause of morbidity and mortality affecting 20,000 infants in the United States yearly. Known BPD risk factors include prematurity, respiratory support, oxygen use, and the presence of a patent ductus arteriosus (PDA). PDA increases BPD risk due to increased pulmonary blood flow which also occurs in the presence of an atrial septal defect (ASD). The extent to which an ASD impacts the risk of BPD is largely unknown. Hypothesis: Evaluate the association between ASD and BPD risk in premature infants. Methods: We used electronic medical record data from >950,000 infants in 362 neonatal intensive care units (NICUs) in the US managed by Pediatrix Medical Group (2004 - 2013) to identify infants 24-30 weeks gestational age (GA) and <1250 g birth weight (BW). We excluded infants with major anomalies including heart defects other than ASD or PDA. We defined BPD as the need for supplemental oxygen or respiratory support continuously from corrected GA 36-0 to 36-6 weeks. We predicted risk of BPD at 6 postnatal ages (1, 3, 7, 14, 21, and 28 days) using the NICHD Neonatal Research Network BPD risk calculator. We then developed separate logistic regression models conditioned on NICU center to evaluate the association between ASD and BPD adjusting for baseline BPD risk at the 6 time points. We repeated each model controlling for therapeutic interventions (PDA ligation, diuretics, pre- and postnatal steroids). Results: We identified 36,842 infants; 1257 (3%) had an ASD. Median GA and BW were 27 weeks (25th, 75th %ile 26, 29) and 940 g (765, 1091); 50% were male. BPD was more common in infants with ASD [593/1257 (47%) vs. 10,739/35,585 (30%), p<0.001]. Adjusted odds of BPD were higher in infants with ASD (Table). Conclusions: A diagnosis of ASD was associated with BPD risk in premature infants . Further studies should determine the impact of ASD size, pulmonary blood flow and resistance, and right ventricular compliance on the risk of developing BPD.