Sir.—Bell et al1 have to be commended for focusing their attention on the long-term pulmonary outcome of two patients born with sublethal forms of lung hypoplasia. There is remarkably little information available in the literature on what happens to lung structure and function of these infants and children as they develop. Clinicians all too often assume that lung structure has normalized when the patient is asymptomatic and has a clear chest roentgenogram and normal pulmonary function study results. A very instructive case was reported in detail by Thurlbeck et al.2 Their patient was born with a left-sided diaphragmatic hernia and hypoplastic lung documented at the time of the successful surgical repair. His chest roentgenogram and pulmonary function study results were normal at 1 year of age and he died in an accident at age 5 years. At necropsy, the volumes of both lungs were normal, but the