We aimed to determine if prematurity and lower birth weight are associated with poorer lung function in a non-western developed setting with less marked confounding by socioeconomic position. Using multivariable linear regression in Hong Kong's "Children of 1997" birth cohort, adjusted associations of prematurity and birth weight with forced expiratory volume in 1 second (FEV 1), forced vital capacity (FVC), and forced expiratory flow at 25-75% of the pulmonary volume (FEF 25-75%) at ~17.5 years were assessed. Associations for birth weight were stronger in boys for FEV 1 (boys: 0.31 L, 95% confidence interval (CI) 0.24 to 0.38, girls: 0.18 L, 95% CI 0.12 to 0.25), FVC (boys: 0.36 L, 95% CI 0.27 to 0.44, girls: 0.22 L, 95% CI 0.15 to 0.28) and FEF 25-75% (boys: 0.35 L, 95% CI 0.21 to 0.49, girls: 0.22 L, 95% CI 0.09 to 0.34) adjusted for age, socioeconomic position and infant and maternal characteristics. Similarly adjusted, preterm birth (compared to full-term birth) was associated with lower FEV 1 /FVC and FEF 25-75%. Thus, associations of lower birth weight, especially in boys, and prematurity with poorer lung function at 17.5 years were found. Identifying underlying mechanism might contribute to the improvement of pulmonary health and the prevention of adult respiratory illness. 75%)) in extreme preterm births while fewer studies have focused on lung function in late preterm births 6,19,22-26. Evidence from twin studies, which are less open to confounding by family socioeconomic position, is limited, but suggests lower birth weight is associated with poorer lung function, i.e. lower expiry in the first second