A simple cyst on the ovary is a fluid-filled sac that forms on or inside an ovary. Simple cysts are usually a large follicle that has continued to grow after an egg has been released. They are the most common type of ovarian cyst and are usually benign. Simple cysts are also known as functional cysts, which occur as a result of ovulation. They can be a sign that your ovaries are functioning as they should. Simple cysts are usually harmless, and they often disappear on their own within two to three menstrual cycles. However, if they become large, they can cause complications such as painful twisting of the ovary, called ovarian torsion. Regular pelvic exams help ensure that changes in your ovaries are diagnosed as early as possible. If your provider finds a cyst that’s concerning, follow their recommendations for next steps.