Several studies have suggested that high intake of fats and fat-rich foods may increase the risk of ovarian cancer. The authors examined these relations in the Nurses' Health Study cohort. Dietary intake was assessed in 1980, 1984, 1986, and 1990 by using a self-administered food frequency questionnaire. Food data were used to calculate intake of various fats and fatty acids. For best reflection of long-term intake, an updated, cumulative, averaged measure of fat intake was used to predict incidence of ovarian cancer. Between 1980 and 1996, 301 incident cases of invasive epithelial ovarian cancer were confirmed among the 80,258 participants who completed the baseline food frequency questionnaire. There was no evidence of a positive association between intake of any type of fat and ovarian cancer risk, even after adjustment of fat subtypes for one another. Women in the highest quintile of total fat intake were not at increased risk compared with those in the lowest quintile (multivariate relative risk = 1.03, 95 percent confidence interval: 0.72, 1.45, p for trend = 0.97). Intakes of fat-rich foods were also not appreciably associated with ovarian cancer risk, although an increase in risk with frequent intake of eggs was observed. Overall, results suggest no association between intake of any type of fat and ovarian cancer.