The prediction of profile changes after surgery poses a problem due to the variability of the soft tissue and the differences in soft-tissue translations relative to osseous changes. This study examined the accuracy of computer predictions of such soft-tissue changes. Twenty-five patients with mandibular retrognathia were examined before and after orthognathic surgery. Changes in soft-tissue reference points were correlated to translations of hard-tissue references in the sagittal and vertical planes, and the measurements from these patients were compared to results predicted in preoperative planning by the cephalometric and video imaging program Dentofacial Planner. In surgical treatment involving advancement of the mandible, the mean operative advancement of the osseous pogonion was 6.06 mm. The corresponding movements of soft-tissue references, expressed as percentages relative to the movement of the osseous pogonion in the sagittal plane, were 98.4% for the soft-tissue pogonion, 93.6% for the soft-tissue menton, and 49.0% for the soft-tissue labrale inferior. The same measurements were carried out in the vertical plane and the changes in soft-tissue references were compared to those predicted in preoperative planning using the Dentofacial Planner. The predicted images were perceived as agreeing with the actual image most frequently in the lip and nasal area, while the highest degree of error was seen in the submental region. An overall predictability of more than 80% can be attained by planning mandibular advancement operations for correction of mandibular retrognathia using the Dentofacial Planner.