Endometrial stromal sarcoma usually has the gross appearance of a single nodule, multiple masses, or a poorly demarcated lesion with occasional cystic degeneration; however, a multilocular form has not been described in the literature. We report the case of a 25-year-old woman with a cystic multilocular lesion with thin septae measuring 8 cm, discovered by a pelvic ultrasonography. Grossly, it was a multicystic mass located in uterine fundus that was attached to myometrium and showed infiltrating borders. We propose that cystic endometrial stromal sarcoma should be included in the differential diagnosis of cystic uterine tumors.