Epithelial ovarian cancer kills more women per year than all other gynecologic cancers combined. Pregnancy, oral contraceptive use, and tubal ligation decrease the risk of the disease, whereas risk is increased for women whose family history is consistent with one of the familial ovarian cancer syndromes. Several theories have been postulated concerning the etiology of ovarian cancer, including the incessant ovulation theory and that based on the model of hypergonadotropic hypogonadism. Chromosomal abnormalities and allele losses have been described in ovarian cancers. Involvement of oncogenes and tumor suppressor genes has been investigated as well. Genetic linkage studies are ongoing in families whose history is consistent with one of the familial ovarian cancer syndromes.