An ovarian cyst is a fluid-filled sac (follicle) that contains a maturing egg; it forms on the ovary's surface, then disappears not long after it releases the egg. If a mature egg is not released or if the sac reseals after the egg is released, the sac can swell up with fluid, forming a functional ovarian cyst.

Most functional ovarian cysts do not cause symptoms and will go away by themselves. Some may rupture, twist, or bleed, which can cause severe pelvic pain.

By	Healthwise Staff
Primary Medical Reviewer	Sarah Marshall, MD - Family Medicine
Specialist Medical Reviewer	Kirtly Jones, MD - Obstetrics and Gynecology
Last Revised	October 12, 2010