Distal radius malunions are common complications in patients with distal radius fractures. There are several possible therapies; correction must be perfect in all three spatial planes. Planning and three-dimensional (3D) printing aid the surgeon in performing a customized, personalized dorsal-opening osteotomy to correct a distal radius malunion. We report the case of such a patient; surgery was assisted by 3D-printing of guides for correction of the distal radius malunion. The drilling and cutting guides allowed us to perform a standardized intervention, reducing the need for intraoperative fluoroscopy and eliminating all steps that usually require subjective decisions.