Summary: Case report of a 51 year old man involved in a motor vehicle accident presenting with multiple thoracic wall injury, including bilateral first rib fractures. He slowly developed a right sided Horner's syndrome due to a right paravertebral haematoma. The initial imaging did not display any carotid injury, however the developing right paravertebral haematoma was not initially reported. We review the anatomy and pathophysiology of this well-known but rare condition to show how first rib fractures should raise suspicion of Horner's syndrome irrespective of the presence or absence of any underlying blunt carotid injury. Keywords: Trauma, First rib fracture, Horner's syndrome, Blunt carotid injury