Intra-articular fractures of the base of the first metacarpal (Bennet fractures) are prone to dislocation and require surgical reduction and fixation to prevent secondary degenerative joint disease and chronic dysfunction. Therefore, a prompt diagnosis is necessary, mostly achieved by conventional roentgenograms. We report the case of a 62-year-old man in whom a Bennet fracture was highly suspected on ultrasound (US) examination realized after a fall. Standard radiographs, obtained after US to confirm the diagnosis, were interpreted as normal. A computed tomography was then performed showing a typical Bennet fracture. This case report demonstrates that a careful assessment of bones must be an integral part of any routine musculo-skeletal US examination, particularly in post-traumatic patients. US can detect bone fractures where radiograph is not discriminating.