Endometriosis was first described by Russel more than one-hundred years ago and still remains a clinical entity of difficult comprehension, with totally aberrant symptomatology, particularly in extra-genital situations. The present article describes a clinical case of recurring right-sided catamenial pneumothorax in a 45 year-old caucasian woman. In her last episode of right chest pain the X-ray film showed, besides the presence of a pneumothorax, a nodular image, later identified by CT scan as being a transdiaphragmatic hernia with hepatic content. The patient was then submitted to diagnostic and therapeutic thoracotomy and the diaphragmatic endometriosis was confirmed. Finally, a total hysterectomy with bilateral salpingo-ophorectomy was performed and the patient's condition remained uneventful with combined hormone therapy. The clinical presentation, pathogenesis, and therapeutic resolution of this nosological entity are briefly discussed.