Emphysema and bronchiolar obstruction were found in the necropsy specimens from 42 of 84 patients with cystic fibrosis of the pancreas. Significant parenchymal destruction could be demonstrated in only three cases. In contrast, widespread severe dilatation of respiratory bronchioles and alveolar ducts was present in 29 of the older infants and children, and less extensive, moderate dilatation was seen in an additional 13 cases. Eleven patients also had morphological evidence of bronchiolar scarring and stenosis. Because of the chronic pulmonary infection in these patients, it is unlikely that the structural changes in peripheral airways are clinically significant. Nevertheless, this widespread dilatation may be responsible for the physiological and radiographic evidence of emphysema. Furthermore, the lobular dilatation in these young patients may be an antecedent of destructive emphysema in the adult.