OBJECTIVE To provide a quantitative assessment of the association between oral contraceptive (OC) use and ovarian cancer using results from the published literature. METHODS We conducted a MEDLINE literature search for all epidemiologic studies of OC and ovarian cancer published in English between 1970-1991. The reference list for each article was reviewed to locate additional published articles. METHODS We included 20 studies in which a relative risk and either a standard error, confidence interval, or P value was reported, or sufficient data were presented to allow us to calculate these measures. METHODS We summarized the findings using weighted averages and regression analyses. We found a summary relative risk of 0.64 (95% confidence interval 0.57-0.73) associated with ever-use of OC, indicating a 36% reduction in ovarian cancer risk. The risk of ovarian cancer decreased with increasing duration of OC use; we noted a 10-12% decrease in risk with 1 year of use and approximately a 50% decrease after 5 years of use. The reduced risk was present among both nulliparous and parous women and it appeared to last for at least 10 years after cessation of use. Although most studies assessed the use of cessation of use. Although most studies assessed the use of OC formulations from the 1960s and 1970s, data from the Cancer and Steroid Hormone Study indicate that the decreased ovarian cancer risk may also be present with current lower-dose formulations. CONCLUSIONS The protective effect of OC against ovarian cancer risk should be considered in a woman's decision to use OC.