Obstructive lung diseases remain as important complications of preterm birth, usually attributed to a combination of lung immaturity, oxygen therapy and ventilator support. This is particularly true for low birth weight infants with severe respiratory neonatal disease; however, preterm infants that did not initially demonstrate significant respiratory neonatal disease also have reduced lung function when examined later in life, suggesting that prematurity alone could generate a persistent obstructive disease. Recent data have shown a significant reduction in maximal expiratory flows in healthy premature infants compared with control infants and reference values, when tested in the first months of life. Reduced expiratory flows were associated with male sex, low gestational age, smoking exposure and increased weight gain. The mechanism for this has not been determined and could result from smaller airways, a decrease in pulmonary elastic recoil secondary to abnormal alveolarisation of the lung parenchyma, as well as more compliant airways.