OBJECTIVE The 3-dimensional (3D) accuracy of computer-assisted planning (CAP) of segmental maxillary osteotomies has seldom been reported with a comprehensive 3D analysis. The aim of the present study was to measure the accuracy of computer-planned segmental maxillary surgery and to identify the factors associated with accuracy. METHODS The present retrospective, cross-sectional study investigated cone-beam computed tomography (CBCT) scans of patients who had undergone segmental maxillary osteotomy with CAP at a single center from January 2013 to October 2019. The predictor variables were age, gender, diagnosis, CAP method, type of maxillary segmentalization, surgeon, surgical sequence, and magnitude of planned and actual movements. The primary outcome variable was surgical discrepancy (linear differences between the actual and planned maxillary movements using CAP in the x, y, and z coordinates) at various 3D landmarks. The mean difference and absolute mean difference (AMD) were computed to estimate the direction and magnitude of the discrepancies. In addition, a 2.0-mm threshold of surgical discrepancy was used to determine clinically acceptable accuracy. The association between the predictor and outcome variables were analyzed statistically using correlation and regression analyses. RESULTS The sample included 63 patients (mean age, 20.1 years; 42.9% male). The surgical discrepancy was similar for 2- and 3-piece segmental maxillary osteotomies. Overall, the AMD for all patients was 0.96 ± 0.69 mm transversely, 1.23 ± 0.83 mm vertically, and 1.16 ± 0.80 mm anteroposteriorly (P < .01 for all). The discrepancy between the actual and planned movements was within 2.0 mm for more than 80% of cases. The major predictor variable that affected surgical discrepancy was the magnitude of the actual surgical movements (P < .01). CONCLUSIONS 3D CAP showed clinically acceptable accuracy for segmental maxillary osteotomies comparable to that of nonsegmental cases. Although the magnitude of actual surgical movements was shown to affect surgical accuracy, the sources of surgical discrepancies requires further investigation.