We reported a case of severe endometriosis with frequent recurrent catamenial pneumothorax and pleural effusion. A 38 year-old nulligravida women had repeatedly a catamenial pneumothorax with natural cure. She was referred to Otsu Municipal Hospital complaining of chest pain, strong dyspnea and severe dysmenorrhea. Chest CT scan findings led to a diagnosis of catamenial pneumothorax of the right side. A right thoracoscopy procedure revealed multiple blue berry colored spots on the right side tendon of the diaphragm. Partial resection of the diaphragm including the spots was performed under video assisted thoracoscopic surgery. 4 months later, the patient underwent laparoscopic surgery for pelvic endometriosis and an ovarian chocolate cyst. The pelvic endometriosis was shown to consist of severe lesions and Re-AFS stage IV disease (Re-AFS score 45). After 5 months following the video assisted thoracoscopic surgery, she had frequent recurrent pneumothorax and pleural effusion in the right side thorax. In our case, the measurement of serum CRP (C - reactive protein) was suspected to be helpful for early detection of recurrent endometriosis-related pneumothorax and pleural effusion. Conservative therapies of thoracentesis and pleurodesis were not effective for recurrent pneumothorax and pleural effusion. She had acquired partial remission of pneumothorax and pleural effusion following the second Gn-RH agonist administration. Following oral dienogest therapy after the fourth Gn-RHa administration, she had acquired no recurrence of catamenial pneumothorax and pleural effusion over 10 months. We concluded that serum CRP measurement is suspected to be useful for early detection of endometriosis-related pneumothorax and pleural effusion. Gn-RH agonist and oral dienogest were found to be useful treatment. [Adv Obstet Gynecol, 63 (1) : 18-23, 2011 (H23.2)]