There are several causes of abnormally enlarged ovaries. Some are considered functional (non-harmful). During the menstrual cycle, the ovaries enlarge as follicles mature and prepare for ovulation. Enlarged ovaries may also be a sign of ovarian cancer, a malignant condition, though this is not a common cause. Therefore, if you experience any abnormal signs of ovarian enlargement, you should consult a doctor to rule out malignant causes. Below are some reasons for abnormally enlarged ovaries.