A number of studies have documented the familial aggregation of lung cancer; there is at least one report that female reproductive cancers are also increased in these families. To determine if the risk exists for all reproductive cancer sites, we conducted a nested case-control study of lung cancer incidence in a cohort of 41,837 women ages 55-69 years. Women were recruited by mail and asked to provide information on education, occupation, smoking habits, physical activity, and family history of specific cancer sites among female relatives. Four year follow-up for cancer incidence was conducted using a state-wide tumor registry. Compared to random controls (n = 1900), cases (n = 152) were more likely to have reported at baseline a sister affected with cancer of the uterus [crude odds ratio (OR) = 3.4, 95% Cl = 1.7-7.0, P less than 0.01], cervix (OR = 3.2, 95% Cl 1.2-8.6, P less than 0.05), or cancer at any site (OR = 1.6, 95% Cl 1.1-2.4, P less than 0.05). A family history of an affected mother with a female reproductive cancer was also more common among the cases, but not statistically significant. Cases were less educated, more likely to work in a technical/industrial setting, less physically active, more likely to smoke, and to smoke for a longer period of time than the controls (all P less than 0.01). These differences reduced the magnitude of the family history risk indicators; only the combined category of reproductive cancer at all sites among sisters remained statistically significant. Additional family studies should be done to assess environmental factors in the relatives of the cases and controls to disentangle the influence of shared genes and shared environmental factors in these associations.