To clarify etiology of lung cancer in nonsmoker females, various studies have been done. Particularly, host factors and environmental tobacco smoking (ETS) of females have been emphasized. However, traditional epidemiological data showed controversial results of sex or gender differences in lung cancer susceptibility and suggest presence of some confounders. One of them is that most of epidemiology studies are based on self-reports for ETS. To prevent misestimate effects of ETS via the self-report, exposure monitoring of ETS is required. On the other hand, focusing on genetic polymorphisms in metabolic enzymes and DNA repair, molecular epidemiological studies have been done in nonsmoker females. Therefore, this review considered: 1. gender differences in lung cancer; 2. effects of passive smoking on lung cancer; 3. exposure monitoring of ETS including genetic risks of lung cancer to clarify etiology of lung cancer in the nonsmoker females with molecular epidemiological discussion.