Patient: Female, 30Final Diagnosis: Thoracic endometriosis syndromeSymptoms: Abdominal painMedication: —Clinical Procedure: Videothoracoscopic pleurodesisSpecialty: PulmonologyObjective:Rare co-existance of disease or pathologyBackground:Catamenial pneumothorax (CP) is a spontaneous pneumothorax commonly associated with menstrual periods. Endometrial tissues most commonly involve the pelvic region. However, after the pelvis, the lungs are most frequently involved. Thoracic endometriosis should always be suspected in young women presenting with CP.Case Report:A 30-year-old woman with history of endometriosis presented with chief complaint of umbilical pain. A computerized tomography (CT) scan of the abdomen and pelvis was performed, which showed an incidental finding of a large right-sided pneumothorax. Chest X-ray imaging showed 50% pneumothorax. A right-sided chest tube was placed, and after the procedure, a chest X-ray image showed expansion of the right lung. The patient was readmitted for elective resection of an umbilical mass and was again incidentally found to have a recurrent pneumothorax on the right side. She underwent videothoracoscopic pleurodesis with pathology, establishing the diagnosis of catamenial pneumothorax.Conclusions:Thoracic endometriosis resulting in catamenial pneumothorax should be suspected in young women of child-bearing age. Treatment options still under debate include endoscopic resection and videothoracoscopic pleurodesis followed by gonadotrophin-releasing hormone (GnRH) therapy to reduce the rate of postoperative recurrence.