A 47-year-old woman was admitted to our hospital because of two episodes of right pneumothorax. After continuous suction through a thoracic drain, a computerized tomographic scan showed that air was still trapped between lung lobes. Video-assisted thoracic surgery revealed a bulla on the visceral pleural of the upper lobe (S2) and several dark-red spots and white-coated lesions surrounding a defect of the diaphragm. The involved portions of the diaphragm and of the lung were excised. Microscopic examination of the excised specimens showed endometriosis. Catamenial pneumothorax may be caused by intrathoracic endometriosis, but very few cases in which pulmonary or visceral pleural endometriosis was demonstrated histologically have been reported.