The clinical study of the treatment of a sample of Class II malocclusions was made. This information from both successful and unsuccessful Class II malocclusion correction was recorded. The objective of the study was to determine whether there are predictive characteristics of Class II cases that could give, with reasonable accuracy, an indication of those Class II malocclusions that would more readily respond to treatment and those that would have less chance of conventional treatment being successful. This information could give the orthodontist differential diagnostic guidance before starting treatment to determine whether alternative treatment strategy should be considered. The study used five very important cranial and dental cephalometric measurements that individually had significance, but no predictive value. However, these measurements, when combined, and given a weighted value that reflected a relative importance of each criteria, were found to collectively give a predictive capability in determining whether the case was favorable for Class II correction. The five angles selected were (1) the Frankfort mandibular plane angle (FMA); (2) the point A nasion point B, (ANB) angle; (3) the occlusal plane, Frankfort plane angle; (4) the Frankfort-mandibular incisor (FMIA) angle; (5) the sella-nasion-point B, (SNB) angle. The Probability Index is the sum of the weighted values of the five cranial, and dental angles and seems to have significant predictive value in the differential diagnosis and treatment planning of the Class II malocclusion.