BACKGROUND: Fatty acids impact obesity, estrogens, and inflammation, which are risk factors for ovarian cancer. Few epidemiologic studies have investigated the association of fatty acids with ovarian cancer. METHODS: Within the European Prospective Investigation into Cancer and Nutrition (EPIC), 1,486 incident ovarian cancer cases were identified. Cox proportional hazard models with adjustment for ovarian cancer risk factors were used to estimate HRs of ovarian cancer across quintiles of intake of fatty acids. False discovery rate was computed to control for multiple testing. Multivariable conditional logistic regression models were used to estimate ORs of ovarian cancer across tertiles of plasma fatty acids among 633 cases and two matched controls in a nested case-control analysis. RESULTS: A positive association was found between ovarian cancer and intake of industrial trans elaidic acid [HR comparing fifth with first quintile(Q5-Q1) = 1.29; 95% confidence interval (CI) = 1.03-1.62; P (trend) = 0.02, q-value = 0.06]. Dietary intakes of n-6 linoleic acid (HR(Q5-Q1) = 1.10; 95% CI = 1.01-1.21; P (trend) = 0.03) and n-3 α-linolenic acid (HR(Q5-Q1) = 1.18; 95% CI = 1.05-1.34; P (trend) = 0.007) from deep-frying fats were also positively associated with ovarian cancer. Suggestive associations were reported for circulating elaidic (OR comparing third with first tertile(T3-T1) = 1.39; 95% CI = 0.99-1.94; P (trend) = 0.06) and α-linolenic acids (OR(T3-T1) = 1.30; 95% CI = 0.98-1.72; P (trend) = 0.06). CONCLUSIONS: Our results suggest that higher intakes and circulating levels of industrial trans elaidic acid, and higher intakes of linoleic acid and α-linolenic acid from deep-frying fat, may be associated with greater risk of ovarian cancer. IMPACT: If causal, eliminating industrial trans-fatty acids could offer a straightforward public health action for reducing ovarian cancer risk.