This study related respiratory illness documented in the first 2 yr of life to the lung function of 618 men and women with a mean age of 70 yr living in Derbyshire, England. Pneumonia before 2 yr of age was associated with a lower mean FEV1, adjusted for age and height. In men, the difference was -0.65L (95% CI: -1.02, -0.29; p = 0.0005). This estimate did not diminish after adjustment for smoking and asthma. In women, the reduction in mean FEV1 associated with pneumonia before 2 yr of age was smaller and nonsignificant. Bronchitis, measles, and whooping cough before 2 yr of age were not associated with diminished adult lung function in either sex. The findings in men support a causal relationship between pneumonia in early childhood and COPD in late adult life.