The analysis of autopsy data from 1928 to 1972 shows that the relative frequency of lung cancer has undergone a fourfold increase till about 1962, and has since then remained practically constant. The right lung is more often the seat of carcinoma than the left lung and the upper lobes more often than the lower lobes. For females the upper-lower lobe asymmetry is not significant. The nonuniform distribution of tumor sites is explained on the basis of ‘contact hypothesis’. Some age and sex factors have been studied.