We evaluated the impact of recreational and occupational physical activity on ovarian cancer risk using data from a population-based case-control study of 442 cases with histologically confirmed incident ovarian cancer and 2,135 controls aged 20-76 years, conducted in 1994-1997 in Canada. Frequency and intensity of physical activity were collected through self-administered questionnaires. Compared to women in the lowest tertiles of moderate, vigorous and total recreational activity, those in the highest tertiles had multivariable-adjusted odds ratios (and 95% confidence intervals) of 0.67 (0.50-0.88), 0.93 (0.70-1.24) and 0.73 (0.58-0.98), respectively. There were statistically significant trends of decreasing risk with increasing levels of moderate and total recreational activity, with similar patterns for premenopausal and postmenopausal women. A significant reduction in risk associated with higher level of moderate recreational activity was observed for serous, endometrioid and other but not mucinous types of tumors. The analyses in one province with the largest number of cases and controls indicated that occupational activity was associated with reduced ovarian cancer risk by lifetime activity and by various life periods (early 20s, early 30s, early 50s and 2 years before interview). Our study suggests that occupational and regular moderate recreational physical activity reduce ovarian cancer risk.