1. Cephalograms of 102 children with normal occlusion (Group 1) and 874 children with various malocclusions were analyzed to determine which measurements would produce the highest correlation against the displacement of the molar relationships. 2. Molar displacement was measured directly on the study casts, and an average of the measurements of the right and the left sides was obtained. 3. The malocclusion sample was divided into groups according to molar displacement: 214 neutroclusion cases (Group 2), 624 distoclusion cases (Group 3), and 36 mesioclusion cases (Group 4). 4. The mean value of the anteroposterior dysplasia indicator (APDI) in the normal group was 81.4 degrees, with a standard deviation of 3.79. 5. The APDI reading was obtained by tabulating the facial angle plus or minus the A-B plane angle and plus or minus the palatal plane angle. 6. Among the measurements tested, the APDI was found to show the highest correlation against the molar displacement, with a correlation value of 0.643. 7. The four variable that produced the highest correlation coefficient value--that is, the ANB angle (-0.495), the A-B pland angle (0.566), the "Wits" appraisal (-0.639), and the APDI (0.643)--were subjected to a study of their frequency distribution patterns. High percentage of overlapping of the two extreme groups (distoclusion and mesioclusion groups) were found in the above variables, with the exception of the APDI. 8. A discussion of the differential diagnostic value of the APDI was presented, together with illustrations and various clinical examples.