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 significantly reduces the overall planning time. The osteotomies were performed according to the results of the computer-aided planning. The first 1 year postoperatively an increase of pro-nation from 40° to 70° at expense of supination from 95° to 90°. The patient was practically pain free and reported functional improvement. The second case showed 6 months postoperatively an improvement of supination from 15° to 40° with and of pronation from 50°to 60°. The computer-assisted operation planning facilitated the quantification of combined axial and angular malunions which were difficult to detect on plain radiographs, and reduced preoperative planning time.