A case of catamenial pneumothorax with diaphragmatic and pulmonary endometriosis is presented. A 43-year-old, married woman had three times of recurrent right pneumothorax during the period from January to July on 1990. Each episode was apparently related to the onset of the menstruation suggesting catamenial pneumothorax. Right thoracotomy revealed a perforation of the diaphragm and five black spots on the visceral pleura. Involved portion both diaphragm and lung were excised. Microscopic examination of the excised specimens showed endometrial stroma in the diaphragm and subpleural layer of the lung. Although it has been postulated that intrathoracic endometriosis is a possible cause of the pneumothorax, very few cases have been reported in which pulmonary or pleural endometriosis was demonstrated histologically. Surgical and pathologic findings are documented discussing the relationship of both conditions in this report.