Consistent clinical features of catamenial pneumothorax are its recurrent nature, repeated involvement of the right hemithorax, and a temporal relationship to the onset of menstruation. A personal case with endometrial implants and defects of the the diaphragm is presented. A review of the entire 41 cases reported in the literature reveals that the syndrome is more common than previously believed; there is a definite relationship with endometriosis; and the air allowing the pneumothorax does not appear to enter the chest by way of the genital tract, as originally postulated.