Exostosis, also known as osteochondroma, results from a disorder of the growth-plate where bone grows away from the growth axis and forms an irregular projection. This abnormality most commonly occurs around the femur, scapula, humerus, and ribs. Although hemothorax and diaphragmatic rupture are known complications of exostosis growth, we present herein the first known report of an inward-facing exostosis in a 14-year-old boy with hereditary multiple exostosis causing diaphragmatic rupture and a bowel obstruction requiring operation. Most exostoses are asymptomatic and as such require no further treatment. However, when they are threatening to cause mass effects (such as frictional bursitis, local entrapment of vessels, and tendons or nerves) or symptomatic, surgical resection is the appropriate treatment.