Background: Hereditary multiple exostoses (HME) is a genetic musculoskeletal condition causing multiple exostoses. Rib location of exostosis can be complicated by thoracic injuries.

Methods: We report a case of pneumothorax in a 32-year-old man with a partial left-sided pneumothorax caused by an exostosis of the fourth and fifth ribs.

Results: Clinical and radiological presentations allowed a conservative management. A video-assisted thoracoscopic surgery was performed a few weeks later to avoid any recurrence.

Conclusions: Rib exostosis represents an unusual cause of pneumothorax. Any local modification of symptoms or size of the exostosis should lead to investigations in regard to chondrosarcoma transformation.