This investigation evaluated the reliability and validity of three anteroposterior skeletal measurements using the maxillary-mandibular (MM) Bisector, the functional occlusal plane (FOP), and the bisected occlusal plane (BOP) as reference planes in the assessment of anteroposterior discrepancies. Comparisons were made between these measurements in both treated and control samples of Class II Division 1 patients. The data were collected from pretreatment, posttreatment, and 2 years posttreatment lateral cephalograms of 36 Class II Division 1 subjects whose treatment was nonextraction with low or straight pull headgears. Comparisons were made to an untreated control group of 15 Class II Division 1 subjects. The MM Bisector was found to be a highly reproducible reference plane whose greater stability was demonstrated by a lack of change in its cant during growth or during growth and treatment, compared with the BOP or FOP. With the ANB angle used as a standard, and MM Bisector anteroposterior measure was a more reliable and valid indicator of the skeletal anteroposterior relationship of the jaws, especially longitudinally during growth and treatment, than the Wits appraisals made with either the FOP or BOP.