Recent follow-up studies have provided convincing evidence that the foundations of chronic airflow obstruction (CAO) are laid in utero and early childhood. Men born in Hertfordshire and Derbyshire, England, were more likely to have impaired lung function at 60-70 years of age if they had been lighter at birth and if they had had lower respiratory tract infection (LRTI) in the first 2 years of life. Furthermore, they were more likely to have died from chronic obstructive pulmonary disease if they had been lighter at 1 year of age. These findings suggest that impairment of pulmonary growth in utero and early childhood, as a consequence of undernutrition and LRTI, plays an important part in the development of CAO in late adult life. This may be of particular importance for the future respiratory health of developing nations as the additive effects of smoking take hold.