Epidemiologic evaluations of the relationship between anthropometry and ovarian cancer risk have not been conclusive. Using data collected from two large cohorts, the Nurses' Health Study (NHS) and NHSII, we prospectively evaluated the association between waist and hip circumference, the waist-to-hip ratio (WHR), and BMI with risk of epithelial ovarian cancer. Women completed biennial questionnaires assessing ovarian cancer risk factors beginning in 1976 (NHS) and 1989 (NHSII). For the WHR and BMI analyses, 333 and 862 confirmed cases were identified, respectively, through 1 June 2006 (NHS) and 1 June 2005 (NHSII). WHR and waist circumference were not associated with risk (P-trend = 0.63 and 0.65, respectively). There was evidence for a decreased risk with increasing hip circumference among postmenopausal women (P-trend = 0.03), but a suggestive positive association among premenopausal women (P-trend = 0.04) (P-interaction = 0.01). The hazard ratios (HRs) comparing the highest vs. lowest quintile of hip circumference among pre- and postmenopausal women were 1.54 (95% confidence interval (CI) = 0.45-5.23) and 0.66 (95%CI = 0.37-1.16), respectively. BMI was not clearly associated with risk in pre- or postmenopausal women. Results from this large prospective study suggest that hip circumference could be a possible risk factor for premenopausal ovarian cancer, but may reduce risk of postmenopausal ovarian cancer. The differential effect of hip circumference based on menopausal status requires further confirmation.