The objective of this nationwide case-control study was to examine body mass index (BMI), alcohol use, coffee consumption, cigarette smoking, and leisure-time physical activity in relation to epithelial ovarian cancer (EOC) risk. Subjects were 655 newly diagnosed EOC cases and 3899 population controls, all 50-74 years of age at recruitment between 1993 and 1995. Data were collected through mailed questionnaires. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using unconditional logistic regression. Women with a BMI > or = 30 kg/m2 compared with those with a BMI < 22 kg/m2 appeared to have an elevated EOC risk (OR = 1.37, 95% CI: 1.01-1.85), particularly of mucinous (OR = 2.76, 95% CI: 1.15-6.61) and clear-cell histologies (OR = 2.68, 95% CI: 0.96-7.48). The OR for EOC among coffee users reporting > or = 6 daily cups compared with non-users was 0.68 (95% CI: 0.42-1.10). Alcohol consumption was unrelated to EOC risk. Compared to non-smokers the ORs of EOC among current smokers were 0.70 (95% CI: 0.52-0.94) for those who smoked 1-10 cigarettes/day and 0.74 (95% CI: 0.53-1.02) for heavier smokers, while former smokers were at an unaltered risk (OR = 0.83, 95% CI: 0.66-1.04). Reduced EOC risks were observed among women in the highest compared with the lowest physical activity levels both at age 18-30 years (OR = 0.67, 95% CI: 0.52-0.87) and during the last years preceding study enrollment (OR = 0.68, 95% CI: 0.53-0.87). We conclude that women may avoid an excess risk of EOC through maintaining a normal BMI and reduce their risk by participation in leisure-time physical activity. The use of coffee, alcohol, or cigarette smoking does not appear to increase the risk of EOC.