Video imaging can simulate combined orthodontic-orthognathic surgical treatment to assist in treatment planning and patient education. Video imaging predictions were compared with actual posttreatment results for 18 patients who received orthodontic and mandibular orthognathic surgical treatments. Three untreated control subjects were also studied. The locations of 13 soft tissue landmarks relative to horizontal and vertical reference planes were compared between predictions and posttreatment photographs, and significant variation (+/- 5 mm) was found for many of the landmarks. Comparisons of various steps repeated during the prediction process were also completed to test for reproducibility. Relatively small differences, generally less than +/- 2 mm, were attributed to the process of linking the cephalogram and photograph and to the manual steps to create surgical treatment objectives. The largest proportion of the total variation, about 80%, was estimated to arise from inaccuracy inherent in the software program. Other contributions to the total variation likely came from physiologic facial changes over time and nonstandardized head positions in the photographs.