Rupture of the brachial artery associated with radial nerve palsy in a context of exostosis of the proximal humerus has not been described to date in the literature. Our patient was a fourteen-year-old girl with a history of violent pain occurring suddenly with no prodrome or triggering factor. The pain was localized at the level of the proximal left humerus. Physical examination revealed the presence of a hematoma and complete motor radial nerve palsy. The diagnosis was not confirmed by computed tomography with contrast injection but was confirmed by magnetic resonance imaging which eliminated malignant transformation of the exostosis. After checking the neurovascular bundles and evacuating the hematoma, treatment consisted in resection of the exostosis and arterial repair with an autologous venous graft. We discuss the diagnostic and therapeutic challenges which present vascular complications due to exostosis.