A new computerized, cephalometric, orthognathic surgical program (TIOPS) has been evaluated in surgical simulation, prediction and postoperative assessment of precision. Records of 10 consecutive patients admitted for orthognathic surgical treatment were analysed and prediction plans produced by computerized surgical simulation. Predicted and postoperative positions of maxilla and mandible were compared with linear and angular measurements. No statistically significant differences between predicted and postoperative positions could be demonstrated (p greater than 0.05).