The relationship between physical activity and the risk of ovarian cancer was analyzed using data from a case-control study conducted between 1992 and 1999 in Italy. Cases were 1,031 women with incident, histologically confirmed, invasive epithelial ovarian cancer and controls were 2,411 women admitted to hospital for acute non-neoplastic, non-hormonal conditions. Compared to women with the lowest level of occupational physical activity, the ORs of ovarian cancer obtained adjusting for center, year of interview and age for women with the highest level of physical activity were 0.70, 0.52 and 0.64 (all statistically significant) respectively, at ages 15-19, 30-39 and 50-59 years, with significant trends in risk for the 2 youngest age groups. The corresponding ORs became 0.89, 0.67 and 0.76 after further allowance for several co-variates of ovarian cancer, including education, which was positively associated with cancer risk. No significant association was found with leisure-time physical activity though the risk was below unity in women with the highest level of activity. The multivariate OR was 0.44 for women with the highest level of combined occupational plus leisure-time physical activity. The inverse relationship between occupational physical activity and ovarian cancer risk was not heterogeneous across strata of selected co-variates.