Ovarian cancer incidence rates are highest and stable in white populations; in Asia previously low incidence rates may be increasing. Most cases present with disseminated disease, and mortality rates remain high despite the use of aggressive polychemotherapy. Mortality among younger women has decreased, which has been attributed to widespread use of oral contraceptives. Studies consistently show a protective effect of oral contraceptives that increases with duration of use; no dose effect has been identified to date. Risk decreases substantially with increasing numbers of pregnancies; periods of lactation are relatively less protective. Periods of oral contraceptive use are less protective than equal periods of pregnancy. These factors may protect against ovarian cancer due to inhibition of ovulation or due to suppression of another aspect of ovarian function. Hysterectomy and tubal ligation are both protective, perhaps by preventing the ascent of environmental carcinogens that are as yet unidentified. A positive family history substantially increases risk; mutations in the BRCA1 gene may be responsible for about 5% of cases. No other exposures have been consistently associated with disease risk. Whether risk is modified by ovarian damage mediated by dietary galactose is being evaluated; studies to date have conflicting results. The effect of infertility and its treatments on ovarian cancer risk is controversial; two studies suggest that infertility treatments increase risk.