It has been a clinical impression that the retromylohyoid extension in complete mandibular dentures contributes to stability. This hypothesis was tested in six individuals by means of cineradiography and placement of a metal marker in the mandible and dentures during chewing exercises, with and without the relevant denture extension. Analysis of tracings of the movements of the markers revealed that statistically significant differences existed between first and second chewing experiences. Movement in a horizontal plane around a vertical axis, however, was common to all dentures during all chewing. It is concluded that the retromylohyoid extension has a stabilizing effect on complete mandibular dentures.