OBJECTIVE In segmental maxillary procedures, it is imperative to obtain as much of the planned expansion as possible. Lack of obtained expansion, in addition to late relapse after splint removal, can result in relapse of the posterior crossbite. This study investigated the influence of 2 surgical splint designs on achieving the planned transverse expansion in bimaxillary surgery with segmental maxillary procedures. METHODS Forty-two participants were included in a retrospective observational study. All participants had completed virtually planned bimaxillary surgery with 3-piece maxillary segmentation. The primary outcome variable was the transverse expansion obtained, measured as the expansion between the maxillary first molars on preoperative and postoperative cone-beam computed tomograms. The postoperative scan was performed 1 week after surgery with the splint still in place. To test measurement reliability, all measurements were performed twice by the same observer. The primary predictor variable was the planned expansion according to the virtual surgical plan. The primary covariate with influence on the obtained expansion was the surgical splint design. Other covariates of interest included patient age, patient gender, and surgeon. Descriptive and bivariate statistics were performed using Student t tests and linear regression analysis. RESULTS Measurements showed high reliability, with an intraclass correlation coefficient of 0.99 and Bland-Altman plots without systematic errors. The obtained expansion was statistically different from the planned expansion (mean, -0.77 mm; standard deviation, 0.83). Surgical splint design meaningfully influenced transverse expansion: 77% of the planned expansion was obtained with high palatal coverage, whereas 50% was obtained with low palatal coverage. No other covariates influenced the expansion obtained. CONCLUSIONS Not all the planned expansion is obtained during segmental bimaxillary surgery. Use of rigid surgical splints with high palatal coverage considerably improves the amount of expansion obtained and is recommended for segmental maxillary procedures.