During orthodontic-surgical treatment a three-dimensional repositioning of the maxilla is needed after Le Fort I osteotomy. The preoperative planning usually involves a two-dimensional lateral radiograph. However, the lateral radiograph consists of two dimensions, whereas, during surgery, three dimensions have to be considered. Therefore, the third dimension's influence on treatment planning was investigated in a first study. Lateral radiographs were taken of 20 skulls. Impressions were taken of the maxilla and maxillary teeth. Casts were fabricated, and cuts were made in the transverse vertical plane at the level of the tips of the canines and the mesiobuccal cusps of the first molars bilaterally. Calculations of the discrepancies of the position of reference points on the lateral radiograph and on the lateral surface of the maxilla after the transfer from two to three dimensions revealed for the first molar differences up to 3.3 mm. It is possible to reduce these errors by application of the Goettingen concept for three-dimensional positioning of the maxilla using the 'model-repositioning instrument' for cast surgery and the 'three-dimensional double splint method' with condylar positioning during surgical procedure. This instrument and method were applied during treatment of 20 adult patients in a second study, and the position of the maxilla before and after surgery was analyzed. It was found that the planned position of the maxillary dental arch could be transferred from model surgery to actual surgery with an accuracy of ± 1 mm sagittally and vertically. Schlagwörter: Orthognathic surgery, Le Fort I osteotomy, 3-dimensional repositioning, condylar positioning