Bivariate correlations between sex-specific age-adjusted incidence rates of 10 genital and urinary tract cancer sites and lung cancer were calculated. The data base used was that published in the 5th edition of the series Cancer incidence in five continents. The purpose of the analyses was to test the consistency of the data with the hypothesis of a common risk factor for genital cancers and other cancers of the urinary tract and for lung and genital cancers. The results indicate that the incidence of cervical cancer is strongly correlated with that of cancer of the penis, of other cancers of the female genital tract and of chorioepithelioma. In countries at low/intermediate risk for cervical cancer (mostly developed Western countries), the incidence of cervical cancer is also correlated with that of lung cancer in males. The incidence of male lung cancer is, moreover, strongly correlated with cancers of the prostate, penis, testis, bladder and other urinary tract cancers. These analyses support the views that: urogenital cancers in both sexes might share (a) common risk factor(s), which may be certain types of human papilloma-virus; and that cigarette smoking is likely to be a risk factor for most of these cancers in countries where the use of tobacco has been widespread for a long time. Other suggestive etiological conclusions about less well-studied cancer sites are also presented.