The likelihood of exposure to environmental tobacco smoke (ETS) has been shown to vary across sociodemographic characteristics, health behaviors, and the type of smoking restrictions at work. Women may be particularly at risk. The purpose of our study was to assess differences in the likelihood of exposure to ETS at home and at work among an ethnically diverse sample of women age 40 and older in the United States. We used data from the U.S. Women's Determinants Study and restricted the sample to include only nonsmoking women (n = 2326). Unadjusted and adjusted odds ratios (aOR) for exposure to ETS by sociodemographic characteristics, health risk behaviors, and the type of workplace smoking policy were calculated using logistic regression. Exposure to ETS at home was associated with being American Indian/Alaska Native (aOR 1.5, 95% CI 1.0, 2.6), age 40-44 (aOR 1.6, 95% CI 1.0, 2.6) and 45-54 (aOR 1.8, 95% CI 1.2, 2.6), having eighth grade (aOR 2.1, 95% CI 1.3, 3.6) or high school education (aOR 2.2, 95% CI 1.4, 3.3), inadequate fruit and vegetable consumption (aOR 1.5, 95% CI 1.0, 2.1), and not getting screened for breast cancer (aOR 1.5, 95% CI 1.1, 2.0). Women who did not have regular breast (aOR 1.3, 95% CI 1.9, 1.9) and cervical (aOR 2.0, 95% CI 1.5, 5.3) cancer screening were more likely to be exposed to ETS at work. Exposure to ETS at work was higher among women with some high school education (aOR 2.8, 95% CI 1.5, 5.3) and high school graduates (aOR 3.1, 95% CI 1.9, 5.1) and substantially higher for women who worked where smoking was allowed in some (aOR 15.1, 95% CI 10.2, 22.4) or all (aOR 44.8, 95% CI 19.6, 102.4) work areas. Larger effect sizes were observed for the relationship between selected risk factors and ETS exposure at work than for ETS exposure at home. Among individual risk factors, lower education level was most strongly related to ETS exposure at work. The likelihood of being exposed to ETS at work was highest for women whose workplace smoking policies allowed smoking in some or all work areas.