This chapter discusses the risk factors, clinical signs, evaluation, prevention and screening, and treatment of ovarian cancer and ovarian masses. Ovarian cancer is the leading cause of death from gynecological malignancy and the fourth most common cause of cancer death in women. Advancing age is the greatest risk factor. Use of oral contraceptive pills reduces the risk of ovarian cancer by 30 to 60%. A review of women with ovarian cancer compared with women with breast cancer or no cancer found that most women with ovarian cancer complained of the four following groups of non-specific symptoms in the 1-3 months before diagnosis: abdominal pain (30%), abdominal swelling (16.5%), GI symptoms (8.4%), and pelvic pain (5.4%). Transvaginal sonography (TVS) is the examination of choice to establish the diagnosis. In menstruating women, pregnancy, pregnancy complications and functional cysts are the most common causes of ovarian masses.