Forces exerted by the musculature have frequently been implicated in biomechanical relapse following orthognathic surgery; however, until comparatively recently, satisfactory methods of imaging the head and neck musculature were unavailable. The rapid introduction of magnet ic resonance imagers into medical radiology brings into practical reality the opportunity to use this technology in planning and evaluating patients for orthognathic surgery. Potentially, magnetic resonance images can be used to provide the data necessary for three-dimensional, computer-aided modeling.