Bronchopulmonary dysplasia (BPD; part of the spectrum of chronic lung disease of infancy) is a chronic lung disease in which premature infants, usually those who were treated with supplemental oxygen, require long-term oxygen. The alveoli that are present tend to not be mature enough to function normally. It is more common in infants with low birth weight (LBW) and those who receive prolonged mechanical ventilation to treat respiratory distress syndrome (RDS). It results in significant morbidity and mortality. The definition of BPD has continued to evolve primarily due to changes in the population, such as more survivors at earlier gestational ages, and improved neonatal management including surfactant, antenatal glucocorticoid therapy, and less aggressive mechanical ventilation.

Currently the description of BPD includes the grading of its severity into mild, moderate and severe. This correlates with the infant's maturity, growth and overall severity of illness. The new system offers a better description of underlying pulmonary disease and its severity.