There are many causes of abnormally enlarged ovaries. Some causes are considered functional (not harmful). During the menstrual cycle, the ovaries enlarge as mature follicles develop and prepare for ovulation. Enlarged ovaries can also be a sign of ovarian cancer. This is a malignant disease but is not a common cause. Therefore, when there are any unusual signs of enlarged ovaries, you need to see a doctor to check and rule out these malignant causes. Here are some causes of abnormally enlarged ovaries.