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RATIONALE Identifying neonatal and post-discharge exposures among extremely low gestational age newborns (ELGANs) that drive increased pulmonary morbidity and abnormal lung function at 1 year of age proves challenging. OBJECTIVE The NIH-sponsored Prematurity and Respiratory Outcomes Program (PROP), evaluated infant pulmonary function tests (iPFTs) at one year corrected age to determine which demographic and clinical factors are associated with abnormal lung function. METHODS Infant pulmonary function tests were performed on a PROP subcohort of 135 participants following IRB- approved written consent. Demographic data, Neonatal Intensive Care Unit (NICU) clinical care and post-NICU exposures were analyzed for association with iPFTs. MAIN RESULTS A significant decrease in forced expiratory volume at 0.5 seconds (FEV0.5 ) and/or forced expiratory flows at 75% of forced vital capacity (FEF75 ), were associated with male sex and African American race. Clinical factors including longer duration of ventilatory support, exposure to systemic steroids, and weight less than the 10th percentile at 36 weeks post-menstrual age were also associated with airflow obstruction, whereas supplemental oxygen requirement and bronchopulmonary dysplasia were not. Additionally, the need for respiratory medications, technology or hospitalizations during the first year, ascertained by a quarterly survey, were the only post- NICU factors associated with decreased FEV0.5 and FEF75 . Only 7% of infants had reversible airflow obstruction. CONCLUSIONS Neonatal demographic factors, respiratory support in the NICU, and a history of greater post-NICU medical utilization for respiratory disease had the strongest association with lower lung function at one year in ELGANs. This article is protected by copyright. All rights reserved.