Jewish women have been reported to have a higher risk for familial breast cancer than non-Jewish women and to be more likely to carry mutations in breast cancer genes such as BRCA1. Because BRCA1 mutations also increase women's risk for ovarian cancer, we asked whether Jewish women are at higher risk for familial ovarian cancer than non-Jewish women. To determine the effects of 1) Jewish religion and 2) ovarian cancer in a first-degree relative on women's risk for epithelial ovarian cancer, we used data from a population-based, case-control study conducted in 8 geographic regions in the United States from 1980 through 1982. The study group included 471 cases and 4,025 controls. Jewish women were more likely to have familial ovarian cancer than non-Jewish women [odds ratio (OR) = 8.4, 95% confidence interval (CI) = 2.6-28]. The risk of having ovarian cancer appeared to be greater in Jewish women having a first-degree relative with ovarian cancer (OR = 8.81, 95% CI = 2.02-38.23) than in non-Jewish women having a first-degree relative with ovarian cancer (OR = 3.01, 95% CI = 1.61-5.64), but differences between Jewish and non-Jewish women were not statistically significant. Jewish women with no first-degree relative with ovarian cancer had no increased risk for ovarian cancer (OR = 1.27, 95% CI =