Posterior radial head dislocation without an ulnar fracture in an adult is a rare injury. The pathology is often unrecognized initially. The patient's resultant elbow motion becomes severely compromised. Prompt diagnosis and reduction of the dislocation yield excellent results. A review of the biomechanical studies of the elbow ligaments enables us to propose a pathophysiological model of this injury, and a case report and review of the literature are presented.