Endometrial stromal tumor is a rare mesenchymal uterine tumor. We report the case of a patient with endometrial stromal sarcoma and concomitant bilateral endometrioid adenocarcinoma of the ovary in the context of pelvic endometriosis. The patient underwent a complete cytoreduction including total hysterectomy and bilateral adnexectomy, pelvic lymphadenectomy, appendicectomy, infracolic omentectomy, and pelvic peritonectomy. This is the first report to our knowledge that describes a synchronous endometrial stromal sarcoma and bilateral endometrioid adenocarcinoma of the ovary.