Endometrial stromal sarcomas are rare tumors that recur long after initial excision. We report a case of recurrent endometrial stromal sarcoma treated with the aromatase inhibitor letrozole and an overview of research completed to date. A 59-year-old female presented with new abdominal onset pain, fatigue, and nausea. She had a computed tomography that showed a pelvic mass, an enlarged right internal iliac lymph node, an atypical liver hemangioma, and a severe left hydronephrosis. The patient underwent an exploratory laparotomy, and attempted surgical resection of the pelvic mass was attempted. Pathology was consistent with recurrent endometrial stromal sarcoma. Since these tumors are hormonally sensitive, the patient was started on letrozole 2.5 mg daily. The patient had complete clinical and radiographic response by 11 months. After 24 months of therapy, the patient remained free of disease. Endometrial stromal sarcomas are hormonally sensitive tumors. Progestins function to decrease the effects of estrogen on target cells and have been used for primary therapy of endometrial stromal sarcomas. Aromatase inhibitors block peripheral synthesis of estrogen. Letrozole is a type 2 aromatase inhibitor that effectively reduces serum estrogen levels. Letrozole has been described as treatment for endometrial stromal sarcoma. Letrozole is well tolerated and is a good option for long-term management of this disease.