We report the case of a 25-year-old woman with recurrent right-sided catamenial pneumothorax. At thoracoscopy, the diaphragm presented several violet implants with holes. The presence of diaphragmatic endometrial implants was confirmed at pathologic examination. Re-review of the preoperative chest x-ray film showed 8 x 5 and 1 x 1 mm bubbles at the level of the right diaphragm associated with the homolateral pneumothorax, thus suggesting that passage of air from the genital tract through the diaphragm was responsible for the pneumothorax. This may further clarify the pathogenesis of catamenial pneumothorax which remains controversial in the literature.