The present study proposes a method delineating the extent of the anterior displacement of the temporomandibular articular disc through the angle formed by the deepest point in the glenoid fossa, the center of the mandibular condyle and the junction between the end of the posterior band and the retrodiscal tissue. The method was applied to the normal group and TMD group. The TMD group was further divide into 3 groups Group I(little disc displacement), Group II(anterior disc displacement with reduction) and Group III(anterior disc displacement without reduction). The results were as follows. 1. The normal group showed the location of the articular disc within -10-0degree or with a wider allowance, within -10-10degree from the reference line GC. 2. The TMD group showed the disc located within -21.0-125.8degree,with two peaks at 0-100 and 60-800, suggesting that the group may be composed of more than two different subgroups. 3. The threshold point delineating the normal and TMD states was 0degree, because 82.5% of normal group appeared below 0degree and 94.8% of TMD group appeared above 0degree. 4. Since the angular disc displacement tends to increase from Group I to Group III, the angular displacement increases as the overall severiety of the disease increases, and the chance for a reduction of the disc decreases. 5. The normal group, Group I, Group II, and Group III can be categorized into statistically different groups. The normal group and TMD group can be distinguished in reference to 0degree, while the presence-absence of the anterior disc displacement is judged in reference to 10degree, and the probability of the disc reduction can be estimated in reference to 50degree. The present study assesses the location of the articular disc from the sagittal central section offering a supplementary clinical classification. This system provides an additional information concerning the location of the disc, thereby offering an objective mean to evaluate the progress of the disease. Further studies may be needed on the clinical changes according to location of the disc, as well as the relationship between the morphological changes and the anterior or sideways displacement of the disc.