Catamenial pneumothorax is defined as spontaneous pneumothorax occurring within 72 hours before or after onset of menstruation. Although catamenial pneumothorax is the most common clinical manifestation of intrathoracic endometriosis, this latter condition is not universally identified in women with catamenial pneumothorax and cannot fully explain the recurrent and cyclical episodes of pneumothorax. Therefore, the etiology of this syndrome is unknown, although many theories have been proposed to explain it. We describe a 37-year-old woman with recurrent episodes of spontaneous right-sided pneumothorax and chest pain that occurred close to her menstrual periods. The patient's condition did not abate after initial surgical exploration with abrasive mechanical pleurodesis or after hormonal suppressive therapy at an institution elsewhere. The patient was referred to our institution for further evaluation. A second surgical inspection of the pleural cavity and diaphragm disclosed the presence of multiple diaphragmatic fenestrations that were closed surgically at that time. Postoperatively, the patient discontinued hormonal suppressive therapy, and menstrual cycles became regular. Six months after surgery, the patient remains asymptomatic with no evidence of recurrence of pneumothorax. This case supports recent reports that diaphragmatic defects are often present in patients with catamenial pneumothorax. Surgical exploration to inspect the diaphragm and to close all Identified defects should be performed in patients who continue to experience pneumothorax despite effective hormonal suppression.