A cyst is a fluid-filled sac. In most cases a cyst on the ovary does no harm and goes away by itself. Most women have them sometime during their lives. Cysts are rarely cancerous in women under 50. Cysts sometimes hurt - but not always. Often, a woman finds out about a cyst when she has a pelvic exam. If you're in your childbearing years or past menopause, have no symptoms, and have a fluid-filled cyst, you may choose to monitor the cyst. You may need surgery if you have pain, are past menopause or if the cyst does not go away. Birth control pills can help prevent new cysts. A health problem that may involve ovarian cysts is polycystic ovarian syndrome (PCOS). Women with PCOS can have high levels of male hormones, irregular or no periods and small ovarian cysts.