Background <p>Catamenial pneumothorax is a rare condition, occurring in less than 3–6% of female patients with spontaneous pneumothorax. It is thought that ectopic endometrial tissue in the diaphragm undergoes periodic necrosis during the menstrual cycle, leading to air leakage into the thoracic cavity. This process can result in catamenial pneumothorax and, over time, diaphragmatic damage that may cause liver herniation.</p> Methods <p>A 46-year-old female patient who presented to our clinic with a complaint of long-term air leakage was taken to surgery after liver herniation was detected in the right hemidiaphragm on thoracic computed tomography. Intraoperatively, liver herniation due to diaphragmatic damage was observed.</p> Results <p>The diaphragmatic defect was primarily repaired and supported with prolene mesh. No complications developed in the postoperative period and histopathological examination was found to be consistent with endometriosis.</p> Conclusion <p>It should be kept in mind that endometriosis may be one of the rare causes of secondary pneumothorax and liver herniation. These cases are known to be difficult to diagnose, especially in the early stages. To prevent disease progression, surgical intervention should be planned as early as possible, and the diaphragm should be reinforced with a polypropylene mesh.</p>