Background: Computer-assisted 3D planning combined with CAD/CAM-wafers is more and more common in orthognathic surgery. Nevertheless, the adjustment of the vertical position of the maxilla still stays difficult with this method. Fixation of the mandible to the zygoma using osteosynthesis as a reference is a possible solution. Objectives: Aim of the study was to evaluate the precision of maxillary movement using CAD/CAM-wafers combined with temporary fixation of the mandible. Methods: 10 bimaxillary operations were virtually planned on base of a CT-scan followed by performing a virtual Le-Fort-I-osteotomy with digital maxillary advancement. For transferring the planned position of the maxilla into the operation site CAD/CAM-wafers were generated. Fixation of the mandible to the zygoma was performed using a conventional wafer representing the habitual occlusion. To evaluate the accuracy of this method pre- and postoperative CT-scans were compared by measuring the 3D-deviation of five occlusal landmarks defined on a scanned digital dental impression which was superimposed to the CT-datasets. Findings: The median deviation over all landmarks was 0.76mm. There was a median deviation of 0.97mm in transversal, 0.62mm in sagittal and 1.05mm in vertical plane. The maximal deviation between planning and postoperative results was 2.03mm in the transversal, 2.23mm in the sagittal and 2.58mm in the vertical plane. There was no significant difference between all 3 planes with a generally high precision itself. Conclusion: The method shows to be very precise with a good clinical applicability. However, using mandible fixation for vertical reference prolongs the surgical procedure for approximately 30-45 minutes. Keywords: orthognatic surgery, 3D planning, CAD/CAM generated splint, accuracy