Objective: To investigate the association between nonoccupational physical activity and the risk of ovarian cancer among post-menopausal women. Methods: The Netherlands Cohort Study on Diet and Cancer consists of 62,573 women aged 55-69 years at baseline. Information regarding baseline nonoccupational physical activity and history of sports activity was collected with a self-administered questionnaire in 1986. After 11.3 years of follow-up, 252 cases of invasive epithelial ovarian cancer were available for case-cohort analysis. Results: In multivariate analysis and compared to women who spent less than 30 min per day on physical activity, the rate ratios (RRs) of ovarian cancer for women who spent up to 60, 90 and >90 min per day were 0.78, 0.86 and 0.72, respectively (95% confidence interval (CI) for the top category, 0.48-1.06; p-trend, 0.15). Women who spent more than 2 h per week on recreational biking and walking had a reduced risk of ovarian cancer (RR = 0.65; 95% CI: 0.41-1.01) compared to women who never participated in recreational biking or walking. Conclusions: These data suggest a modest inverse association between moderate physical activity and ovarian cancer risk. Vigorous physical activity was not associated with ovarian cancer risk. © Springer-Verlag 2006.