Most previous studies of passivesmoking and lung cancer, although suggestive of a positive effect, have had several deficiencies. These deficiencies include sample sizes insufficient to singlydemonstrate significant elevations in risk,limited data on passive smoke exposure inboth childhood and adulthood, and lack ofhistologic review of cases to verify lungcancer diagnosis and to allow analyses bycell type.To more fully evaluate the relationship between lung cancer and passivesmoke exposure in childhood and adulthood, we conducted a large case-controlstudy of lung cancer among nonsmokingwomen.