An exceptional case of posterior dislocation of the ulna at the elbow, associated with fracture of the radial shaft, is reported. Diagnosis was established with anteroposterior and lateral radiographs of the forearm, elbow and wrist. Treatment consisted of closed reduction of the ulnar dislocation and open reduction and internal fixation of the radius with an AO plate. A long arm cast was applied for 3 weeks with the elbow held at 90 °. Six months later full function of the limb had been achieved.