Evidence on dietary risk factors for ovarian cancer is inconsistent, but some studies have suggested positive associations with dietary fat, lactose, and cholesterol and negative associations with green and yellow vegetable intake. By using information from the Iowa Women's Health Study, the authors investigated the association of epithelial ovarian cancer with dietary factors in a prospective study of 29,083 postmenopausal women. Dietary information was ascertained via a food frequency questionnaire mailed to participants in 1986. During 10 years of follow-up (1986-1995), 139 of the women developed incident epithelial ovarian cancer. Incidence of the disease was not associated with dietary fat intake. Lactose and cholesterol showed moderately elevated risks. Multivariable-adjusted relative risks for the lowest to highest quartiles of lactose intake were 1.00, 1.38, 1.25, and 1.60 (p for trend = 0.12). For cholesterol, the corresponding values were 1.00, 1.34, 1.86, and 1.55 (p for trend = 0.06). Consumption of eggs was also associated with an increased risk of ovarian cancer. Multivariable-adjusted relative risks for increasing frequency of egg consumption were 1.00 (<1/week), 1.12 (1/week), 2.04 (2-4/week), and 1.81 (>4/week) (p for trend = 0.04). Total vegetable intake was modestly and inversely associated with the risk of ovarian cancer (p for trend = 0.21). Green leafy vegetable intake was more strongly associated with a decreased risk: multivariable-adjusted relative risks for the lowest to highest intake levels were 1.00, 0.80, 0.87, and 0.44 (p = 0.01). These findings are generally in agreement with the results from previous, mostly case-control studies of diet and epithelial ovarian cancer.