Multiple hereditary exostoses are frequently observed in children, but vascular complications from exostoses in siblings are rare. We report the case of a 10-year-old boy, admitted for dyspnea and chest pain related to a hemothorax due to a right eighth rib exostosis. He was successfully treated by costal resection and chest tube drainage. In retracing his family history, another vascular involvement was discovered. His sister had presented a few years earlier with a spontaneous rupture of brachial artery with radial nerve palsy. To date, only a few cases of spontaneaous hemothorax related to a thoracic exostosis have been described, and to our knowledge, a family association of vascular lesions has not been reported yet. Patients with multiple hereditary exostoses require clinical and radiographic follow-ups during growing years. The main problem is determining the best way to identify dangerous exostoses that may cause vascular lesions. In association with standard surveillance of patients with multiple hereditary exostoses, we suggest performing specific examinations in cases of known thoracic lesions and for patients with a family history of vascular impingement.