This study assessed the possibility of using cervical vertebral bone age determined from cephalometric radiographs to predict mandibular growth potential. The subjects were 2 groups of 20 Japanese girls and young women: one group to derive a formula for predicting mandibular growth potential, the other to compare predicted values with actual values. Each group included subjects in the initial stage of the pubertal growth period and the final stage of growth in early adulthood. A formula for predicting mandibular growth potential that included cervical vertebral bone age and the actual growth of the mandible (condylion-gnathion) was determined with regression analysis. Cervical vertebral bone age, bone age on hand-wrist radiographs, and chronological age were inserted into the formula, and actual values and values predicted with these parameters of the formula for mandibular growth potential were compared. The formula found mandibular growth potential (in millimeters) = -2.76 x cervical vertebral bone age + 38.68. The average error between the value predicted by cervical vertebral bone age and the actual value (1.79 mm) was significantly less (P <.001) than that between the actual value and the value predicted by chronological age (3.48 mm) and approximately the same as that between the actual value and the value predicted by bone age (2.09 mm). The formula derived from this study might be useful for treating orthodontic patients in the growth stage.