The identification of risk factors for ovarian cancer is central to the goal of preventing deaths from this disease. Reproductive and hormonal history clearly modulate the risk of ovarian cancer. Continuous ovulation associated with nulliparity increases the likelihood of ovarian malignancy. Protective factors include conditions that suspend ovulation, such as pregnancy, lactation and oral contraceptive use. Hereditary syndromes account for 10% of ovarian cancer cases. The breast ovarian cancer syndrome is caused by mutations in the BRCA1 and BRCA2 genes and is associated with an 11-40% risk of developing ovarian cancer. The hereditary nonpolyposis colorectal cancer syndrome (HNPCC, or Lynch II) is caused by mutations in DNA mismatch repair genes and carries a 12% risk of ovarian cancer. Due to a lack of adequate screening techniques, women with BRCA1, BRCA2 or HNPCC mutations should consider prophylactic removal of the ovaries and fallopian tubes when childbearing is complete. Genetic polymorphisms are hereditary genetic variations that may act in concert with other genetic, hormonal or environmental factors to potentiate the risk of ovarian cancer. Finally, ovarian cancer risk is altered by environmental and behavioral factors. Further study of the risk factors for ovarian cancer is needed to develop effective preventive strategies.