Endometrial stromal sarcomas (ESS) account for 10-15% of uterine malignancies and are classified into four categories: endometrial stromal nodule (ESN), low-grade endometrial stromal sarcoma (LG-ESS), high-grade endometrial stromal sarcoma (HG-ESS) and undifferentiated uterine sarcoma (USS). Depending on stage, ESS is treated with surgery, hormone therapy, chemotherapy or targeted therapy. A rare complication of ESS with metastatic pulmonary disease is recurrent, bilateral pneumothoraces. The current literature has reported on patients with ESS who either presented with pneumothoraces at their initial diagnosis, and thus were untreated, or after treatment with surgical resection and hormone therapy. There have been no case reports of patients with ESS who presented with pneumothoraces while receiving chemotherapy. Furthermore, there have been no reported cases of patients with HG-ESS presenting with this rare complication. We would like to expand the literature by reporting on two patients with HG-ESS who presented with pneumothoraces while concurrently receiving chemotherapy.