Eight patients with congenital lobar emphysema and eight with congenital cystic adenomatoid malformations were operated upon between 1970 and 1978. A lobectomy was performed in all cases. At follow-up after 3 to 11 years all of the patients without concomitant disease or malformations were subjectively well with a physical performance equal to those of their playmates. Lung function tests indicated lung volumes of about 90% of predicted normal values, indicating some compensatory growth of the remaining lung tissue. Functional impairment owing to loss of lung tissue or residual disease was ruled out by the existence of a normal working capacity and maintenance of the alveolar gas exchange during intense exercise.