Acute bronchiolitis in infancy appears to be associated with persistence of wheezing or subsequent asthma in later life. Chest imaging techniques have demonstrated persistent structural lung damage such as atelectasis, bronchiectasis, and obliterative bronchiolitis among survivors of the more severe forms of bronchiolitis. In addition, in a significant number of survivors without demonstrable structural damage, pulmonary function studies have revealed a spectrum of disturbances including air-trapping, reduced air flow at low lung volumes, hypoxemia (all indicating disease in the small airways), and bronchial hyperreactivity. However, it has not yet been proven definitively whether the relationship between severe bronchiolitis in infancy and chronic obstructive lung disease is causal or noncausal. Further prospective clinical studies are needed to resolve this question.