Endometrial stromal sarcoma (ESS) is a rare malignant tumor that constitutes about 0.2% of all uterine malignancies and 10% of uterine sarcomas. ESS is generally misdiagnosed as leiomyoma or endometrial polyp and typically discovered on histopathological examination postoperatively because of its rarity. Endometrial stromal tumors are composed of cells resembling normal endometrial stroma in its proliferative phase. The histologic diagnosis of the high grade is made if there is a high-grade sarcoma with a high mitotic index and nuclear anaplasia. The mean age of presentation of high-grade endometrial sarcoma is about 61 years with the most common presenting complaint is menorrhagia. The median overall survival for high-grade endometrial sarcoma is 53 months with optimal cytoreduction. A 49-year-old woman P2 L2 presented with nonspecific complaint of discharge and spotting per vaginum. In the present case, the provisional diagnosis by clinical findings as well as imaging was in favor of the inversion of submucous fibroid. Preoperative histopathological examination and immunohistochemistry confirmed the diagnosis of high-grade undifferentiated ESS. Haultain's operation followed by total abdominal hysterectomy and bilateral salpingo-oophorectomy was performed. The patient was referred to another center for radiotherapy. From there, she was lost to follow-up. Rarity of endometrial stromal tumor limits the clinician view to diagnose it preoperatively. We were fortunate to have preoperative histopathological diagnosis of ESS. Furthermore, as ESS is rare and undifferentiated stromal sarcoma is even rarer, literature is lacking on its optimal management. Hence, it is important for all clinicians to keep the high degree of suspicion for ESS while working up any case of abnormal uterine bleeding.