We report about two cases with a combined axial and angular malunion of the radius shaft with functional loss of pro-supination. For the preoperative planning, a computer simulation was developed that allows the quantification of the malunion by comparing the 3-d surface model of the impaired bone with the contralateral anatomy. The proximal parts of the left and right radii are superimposed, while the different positions of the distal parts are used to quantify the malunion. This task is performed fully automatically which reduces the overall planning time. The osteotomies were performed according to the results of the computer-aided planning. The first case showed 1 year postoperatively an increase of pronation from 40 degrees to 70 degrees at expense of supination from 95 degrees to 90 degrees . The patient was practically pain-free and reported functional improvement. The second case showed 6 months postoperatively an improvement of supination from 15 degrees to 40 degrees and of pronation from 50 degrees to 60 degrees . The computer-assisted operation planning facilitated the quantification of combined axial and angular malunions which were difficult to detect on plain radiographs.