This study was performed to compare soft tissue movements resulting from a series of Le Fort I osteotomies with those predicted for the same cases by means of a computerised software package (COG 3.4). The source material consisted of serial lateral cephalometric radiographs for 25 consecutive patients that had received similar Le Fort I osteotomies primarily to correct an antero-posterior skeletal discrepancy. Generally it was found that many of the digitised points on the facial profile were surprisingly well predicted. In addition, the chin and profile changes resulting from mandibular auto-rotation also were reasonably well predicted. However, in a number of cases prediction was less consistent and this was particularly true in the region of the nose and lips. In such instances, initial size, thickness and the existing morphology of the soft tissues appeared to be important factors. The tendency of the software occasionally to 'cross-over' the plots for the upper and lower lip profile made the judgement in this area of predicted profile change difficult in some cases.