An enlarged ovary is an ovary that has expanded past its normal size. The cause of this enlargement is usually cyst formation. Other causes include endometriosis, benign tumors and, rarely, ovarian cancer. Each month, the ovaries normally grow cyst-like structures called follicles. These follicles produce the hormones estrogen and progesterone and release an egg during ovulation. Sometimes numerous follicles can be a finding consistent with polycystic ovarian syndrome (PCOS), or it could be from a regular, normal menstrual cycle