Abstract. A system for interactive, 3–D, craniofacial surgery simulation is presented. It is used for the 3–D simulation of osteotomies of the facial and skull bones and for the prediction of soft–tissue changes caused by bone movement. The result of the simulation process is a 3–D, photorealistic model of the patient’s postoperative appearance that can be viewed from any position. The system is based on the individual preoperative bone structure of a patient’s skull derived from a computer tomography scan and on the patient’s photorealistic, preoperative appearance obtained by a laser scanner. The elasto–mechanical properties of the multi–layer soft–tissue are represented by springs. The model incorporates additional features such as skin turgor, gravity, and sliding bone contact. The prediction of soft–tissue deformation due to simulated bone movement is computed using an optimization approach. Several optimization methods have been tested and compared with rega...