Various modifications have been described to improve the accuracy in intraoral vertical ramus osteotomy (IVRO), but there was not a measurable facility to determine the osteotomy line. The purpose of this study was to evaluate the accuracy of the computer tomography (CT)-based osteotomy template on cadaver mandibles and to assess the outcome after IVRO correcting mandibular prognathism. Four human wet cadaver heads were subjected to a high-resolution multislice spiral CT scan. After the virtual osteotomies in the planning program, the individual osteotomy templates were produced by stereolithography. A stable and secure fit of the stereolithographic templates was achieved via the individual CT-based osteotomy template. The osteotomy lines were performed exactly as planned in the virtual osteotomies planning program. Similar sound outcome was also observed in the clinic. Use of the CT-based osteotomy templates is a safe method for osteotomy. It is rather convenient for vertical osteotomy in IVRO increasing the intraoperative accuracy and efficiency.