Lung cancer currently is the highest cause of cancer mortality in the United States and even surpasses the sum of the next four cancer types in both men and women. In terms of incidence, (the number of new cases of cancer in a given year), lung cancer is second only to breast cancer in women and prostate cancer in men. Lung cancer deaths accounted for 31% and 27% of overall cancer deaths in men and women, respectively, and are more numerous than deaths due to breast, prostate, and colon cancers combined. Graphing lung cancer incidence according to chronologic age of diagnosis on a logarithmic scale demonstrates a straight line for both men and women, indicating that the carcinogenic pathways probably are similar for both genders and that steroid hormones (estrogen and androgens) do not play a major role in carcinogenesis. Lung cancer more typically is present in men than in women, and in African Americans than in white Americans; these disparities in incidence probably are due to smoking patterns. The disparity extends to younger persons as well; young African American men and women have significantly higher lung cancer rates than their white counterparts.