Longitudinal annual changes in lung function (FEV1) with cross-sectional estimates have been compared in the sample of Cracow inhabitants who underwent epidemiological follow-up on chronic nonspecific chest diseases. The annual rate of FEV1 decline was faster in men than in women. Among male smokers the FEV1 decline rate was 30% greater, while in women smokers 9% faster than in non-smokers. The cross-sectional estimates for annual changes differed in both surveys carried out in the interval of 13 years and were not very much consistent with the average longitudinal annual decline observed in the sample. However, the prediction of annual decline across the age groups showed large inconsistencies. They resulted from the curvilinear pattern in lung function decline over the age groups. It was found that the lung function in the elderly appeared to be more homogeneous and the acceleration of decline rates slowed down. There is some evidence that the flattening of the decline curve among elderly might have been influenced by the selection bias.