Background: Pulmonary metastases as an initial presentation of primary uterine low-grade endometrial stromal sarcoma (LGESS) are extremely rare. Optimal treatment for such LGESS has not been established. Case Report: A 30-year-old woman presented with multiple pulmonary metastases on chest X-ray. Chest computed tomography (CT) revealed 11 pulmonary metastases measuring up to 2.8 cm. A uterine mass was detected during the workup and was diagnosed as LGESS by fine needle aspiration. Hysterectomy, right salpingo-oophorectomy, paraaortic and pelvic lymph node sampling, and omentectomy were performed. The left ovary was preserved since the surgery was performed with the aim of palliation and the patient refused to be in surgical menopause. She was then given high-dose megestrol acetate (800 mg/day) for 4 months followed by 200 mg/day for 20 months. The pulmonary metastases of LGESS began to regress with megestrol acetate treatment and almost completely disappeared 17 months after surgery. At this unexpected and satisfactory response to hormonal treatment, the remaining left ovary was also surgically removed. Since the surgery, the patient has been alive without symptomatic pulmonary metastases over 5 years on intermittent treatment of 200 mg megestrol acetate. Conclusion: Megestrol acetate could be suitable as the first-line hormonal treatment for pulmonary metastases from LGESS.