Purpose: to evaluate the accuracy of Computer-Assisted Surgical Simulation (CASS) in the surgery-first treatment of Dentoskeletal Deformities. Materials and methods: Ten patients with different dentoskeletal deformities, were involved in this study. Preoperative clinical evaluation, photographs, study models, and 2D lateral cephalometry were adopted for orthodontic evaluation if the case is eligible for the surgery- first approach. MSCT (in DICOM format), and optical scanning of the study model (in STL format) were adopted and imported to MIMICS software for construction of virtual 3D composite model. The virtual surgical simulation was performed on the light of the preclinical evaluation and preoperative records, then the occlusal splints and surgical guides were designed to transfer the planned surgery to the reality. For evaluation of the virtual surgical simulation 3D cephalometric analysis for the planned and postoperative readings. Result: No significant difference between the planned and postoperative 3D cephalometric analysis. Conclusion: Surgery First cases needed thorough orthodontic and surgical planning. Virtual surgical planning with subsequent designed occlusal splints and cutting guides allow for accurate transfer of the virtual planning into reality.