Catamenial pneumothorax is a spontaneous pneumothorax that occurs predominantly women of child bearing age. We describe a case of a 40-year-old nulliparous woman with medical history significant for endometriosis who presented with severe chest tightness of one-day duration. Chest radiography (CXR) showed a large right spontaneous pneumothorax, what was thought to be a 5.6 cm pleural mass at the right lung base. Following pneumothorax diagnosis, the patient underwent emergent right thoracostomy with pigtail catheter placement. A repeat CXR revealed marked re-expansion of the lung but persistence of a right pleural mass. Follow up computed tomography scan of the chest showed a 33 mm diaphragmatic defect with 5.8 x 4.6 x 3.9 cm area of herniated liver corresponding to the presumed pleural mass. Following complete thoracic imaging, patient underwent video-assisted thoracoscopic surgery, mechanical pleurodesis, and open repair of the right diaphragmatic defect. Intraoperatively, an endometrial implant was noted on the chest wall. On postoperative day three, she began her menstrual cycle and was evaluated by gynecologist who recommended hormonal therapy to reduce risk of recurrent pneumothorax. Due to a persistent air leak, the chest tube was transitioned to a Heimlich valve to facilitate home discharge. The patient was discharged on postoperative day eight, seen as outpatient with resolution of air leak and removal of chest tube.