Smoking-related disease remains a major public-health problem. Large numbers of women continue to smoke, and new smokers are almost as likely to be female as male. Lung cancer is still a largely incurable disease; annual lung-cancer mortality in women exceeds that of breast cancer, and lung cancer now accounts for 12% of all new female cancer cases. The results of several studies suggest that women are more susceptible than men to lung cancer and to conditions that predispose to this cancer, such as chronic obstructive pulmonary disease. There is still much controversy about whether there is an increased lung-cancer risk in women across all populations. Many epidemiological studies have been negative or equivocal when comparing male and female lung-cancer risk. This article is not intended to be a comprehensive review of all epidemiological studies, or of all possible lung-cancer risk factors. Lung-cancer incidence and risk in women are discussed, and evidence for possible mechanisms of increased female risk are presented, including the role of oestrogen in the development of lung cancer.