Consecutive spirographic data of 123 pneumonectomized patients obtained before pneumonectomy, at discharge from hospital, in 1955 (CU1) and in 1975 (CU2) are presented. The mean observation time was of more than 20 years. The loss in inspiratory vital capacity (VC) proved considerably smaller than predicted from transversal studies. It was most pronounced in patients with thoracoplasties and in persons with left remaining lungs. The FEV1 as a percentage of total lung capacity (FEV1%TLC) evidently obviated the qualitative pulmonary function loss over the years. At the same time, data from 25 of 33 patients who died between CU1 and CU2 are reported (mean survival time 15.1 years). The survival rate of the initial group of 168 persons at CU1 was 14% below that of a control group of the same population. Life expectancy in pneumonectomized patients proved to depend more on the quantity of the lung parenchyma available, i.e. the actual inspiratory VC than on the quality as judged from the FEV1 in relation to lung volume.