The purpose of this study was to develop a three-dimensional finite element model of the mandible including the temporomandibular joint (TMJ) and further to investigate stress distributions in the TMJ during clenching. The model consisted of 2088 nodes and 1105 elements, comprising cortical and cancellous bones, articular disc, articular cartilage layer and periodontal ligament. For loading condition, a resultant force of 500 N derived from the cross-sectional areas of the muscles was applied to the model. Compressive stresses were induced in the anterior, middle and lateral areas of the TMJ during clenching, whereas the tensile stresses were induced in the posterior and medial areas. The mean principal stresses on the surface of condyle were -1.642, -0.543, 0.664, -1.017, 0.521 MPa in the anterior, middle, posterior, lateral and medial areas, respectively. The mean stresses on the surface of glenoid fossa were approximately 1/5 to 4/5 those on the surface of condyle, although the patterns of stress distributions were almost similar. In both the articular disc and cartilage layer, the stress distributions were very approximate in qualitative and quantitative aspects. Thus, it is shown that stresses during clenching vary substantially in different structures and areas of the TMJ and that the stresses are reduced by the articular disc and cartilage layer in comparison with actual biting forces exerted by the masticatory muscles, if anatomic relation between various TMJ components is well maintained.