A 39-year-old woman presented with the chief complaint of right-sided chest pressure and shortness of breath with dry cough for 3 days. These symptoms coincided with the onset of her menstrual cycle. Her physical examination was significant for decreased breath sounds at the right lung base. Her chest x-ray showed a moderate sized right pneumothorax extending from the apex to the lung base and a small amount of pleural fluid, findings that were verified by chest CT. The patient was seen by consultants from the pulmonary, obstetrics/gynecology, and thoracic surgery services, who agreed that the clinical diagnosis was catamenial pneumothorax, probably associated with thoracic endometriosis. The patient was discharged on levonorgestrel/ethinyl estradiol tablets, which she opted not to take. Three months later, she had similar symptoms that occurred again at the time of menstruation. Her chest x-ray now showed a 10% right-sided pneumothorax. Catamenial pneumothorax is a rare condition affecting women in their reproductive years. Women with this condition most commonly have right-sided pneumothorax. The proper diagnosis is based on being aware of the existence of this relatively rare condition and relating the symptoms of pneumothorax temporally to the menses.