To provide an improved data base for predicting the soft-tissue changes that accompany mandibular advancement surgery, short- and long-term serial cephalograms from the records of eighteen patients were analyzed. Hard- and soft-tissue landmarks were located on serial tracings and later were reduced to rectangular X-Y coordinates for computer-generated measurement data and statistical analyses. The interpretation of mean value, ratio, and regression equation data showed that the lower lip, inferior labial sulcus, and chin tissues moved forward and downward. The mandibular short-term (mean = 3.7 months postsurgery) horizontal change means were greater than the long-term (mean = 18 months postsurgery) horizontal change means. The posteriorly directed long-term means may result from functional adaptations that follow the short-term surgery-related spatial changes. These data also show the need for long-term prediction data to supplement the short-term data base.