The relation of pulmonary function to aging and cigarette habits has been examined cross sectionally and longitudinally in the Framingham cohort. On cross-sectional analysis, women were found to have lower forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV-1) values than men even after adjusting for height. Their FEV-1 percent was, on the other hand, higher than those of men. As the population aged over 10 years, their FVC and FEV-1 declined 9% to 27% depending upon age and sex. The FEV-1 percent, however, showed a decline only in the older age groups. In a cross-sectional analysis, cigarette smoking showed an inverse association to FVC and FEV-1 percent. Longitudinally, cigarette smokers showed a more rapid decline in FVC in 10 years than nonsmokers. On giving up smoking their FVC became more like that of the nonsmokers. A striking relation of FVC to mortality was noted in both sexes, which is not accounted for by associated cigarette habits.