We examined whether the previously observed lower risk of ovarian cancer among African-American women might be the result of differences in known risk factors. In a population-based, case-control study, sociodemographic, reproductive, and physical risk factors among white (669) and African-American (84) women aged 20 through 69 years with a recent diagnosis of epithelial ovarian cancer (study subjects) were compared with white (1110) and African-American (204) community control subjects. African-American women were more likely to have five or more pregnancies and to have a hysterectomy, whereas white women were more likely to have a family history of ovarian cancer. Yet, the risk and protective factors for ovarian cancer were similar among white and African-American women. As compared with white women, the odds of ovarian cancer among African-American women was significantly lower (odds ratio 0.7, 95% confidence interval [CI] 0.5 to 0.9) and remained somewhat lower after adjusting for known, important risk factors (odds ratio 0.8, 95% CI 0.6 to 1.0). Differences in the obstetric and gynecologic experiences of African-American and white women may explain some of the observed racial variability in ovarian cancer risk, but ovarian cancer risk remained lower among African-American women even after adjustment for these factors.