A solid or fluid-filled sac or pocket, called a cyst, in or on an ovary.

Ovarian cysts are sacs in or on an ovary. The sacs usually are filled with fluid, but they can be solid. Most ovarian cysts go away on their own in a few months. If they don't, they can cause complications.

Most ovarian cysts cause no symptoms. But a large one can cause pelvic pain and bloating. A cyst that grows after menopause can be cancer and needs medical attention.

Birth control pills might keep more cysts from forming. Surgery can remove large cysts.