A review of published reports on lung cancer was done to describe its worldwide epidemiological pattern and to elucidate the contribution of smoking and nonsmoking risk factors in its aetiology. Among lung cancer patients, roughly 98% of males worldwide, and 70-90% of European and American females, reported a history of smoking. Asian women had much lower (6-57%) rates of smoking. Mortality rates among female nonsmokers showed about a four-fold difference, being lowest in India and Japan, intermediate in the USA, and highest among the Chinese. There was some indication that incidence rates among nonsmokers may have increased in some societies in this century. The usefulness of histological comparisons among nonsmokers seemed limited since its distribution did not vary by place or ethnicity; about 70% were adenocarcinomas. In Western populations, younger lung cancer patients were more likely to have been smokers, whereas the opposite was true in Asian populations. Thus the epidemiological patterns of lung cancer in Western and non-Western societies are likely to be different, with nonsmoking risk factors being more important among women in general, and Asian women in particular.