Surgery simulation with a three-dimensional model constructed with stereolithography from digital image data has proven to be useful in the maxillofacial area. The simulation and surgery of Le Fort I and bilateral sagittal split osteotomies were carried out in two patients. The models replicating the facial skeleton with precise internal anatomy facilitated design of the osteotomy and prepa ration of osteosynthesis. Each sectioned segment of the maxilla and mandible was accurately repositioned by transferring the positional relationships of multiple reference points on the model to the bone surface. Cephalograms taken at simulation and after surgery showed little difference in the positions of the landmarks.