The hypothesis that lower respiratory tract infections (LRTI) in early childhood lead to chronic obstructive pulmonary disease (COPD) in late adult life has been difficult to test. However, a unique opportunity arose when records were discovered in the counties of Hertfordshire and Derbyshire, England, that contained information about childhood LRTI recorded 60 to 70 years ago. The lung function of some men still living in these counties was examined. In Hertfordshire men, bronchitis or pneumonia in infancy was associated with reduced mean FEV1, adjusted for age and height. In Derbyshire men, pneumonia before 2 yr of age was associated with a large and highly significant reduction in mean FEV1, adjusted for age and height. These findings were independent of smoking and social class. These data support a causal relationship between LRTI in early life and subsequent COPD.