Our aim is to document a case of endometrioid adenocarcinoma of the ovary found in an endometriotic cyst that was suspected on pelvic ultrasound in a patient with polycystic ovary syndrome, normal Ca125, and a recent history of ovulation induction for IVF. She underwent an exploratory laparotomy with left salpingo-oophorectomy and omental biopsies followed by reexploration, complete staging, and modified radical abdominal hysterectomy and right salpingo-oophorectomy. An endometrioma described as suspicious for malignancy by an experienced ultrasound examiner should prompt immediate referral to a gynecological oncologist irrespective of Ca125 levels especially in women with a history of ovulation induction and endometriosis.