Purpose: The purpose of this study was to determine the predictability when using prebent advancement (PBA) plates in the maxillary osteotomies of maxillomandibular advancement (MMA) surgery. Materials and Methods: A retrospective review of the MMA surgeries at University of Alabama at Birmingham was carried out. Thirty-six obstructive sleep apnea patients who underwent MMA with PBA were included in this study. All cases had fixation of the maxillary osteotomies with KLS Martin PBA titanium plates and screws (KLS Martin, Jacksonville, FL). Lateral cephalometric radiographs were taken within 1 month before surgery (T1), and between 2 to 4 weeks postsurgically (T2). All cephalometric radiographs were analyzed using Planmeca Dimaxis Imaging Software (Helsinki, Finland). Vertical and horizontal measurements were made to several skeletal landmarks including Sella (S), A point (APT), and upper incisor (UPI). The amount of advancement was measured through pre- and postoperative lateral cephalographs and compared with the magnitude of the advancement plates used. Results: All data of 36 patients were included and used for statistics. The data showed that the mean difference was 0.74 mm (advancement is more than the size of the PBA plates) and the mean percentage difference was 11.35%. Fifty percent of the cases had the magnitude of advancement within 1 mm of the PBA size. The predictive analysis found that the PBA size was a significant predictor for the advancement achieved (P < .0001) but not the absolute difference between the advancement achieved and the plate size (P = .0726) and the relative advancement difference (P = .0612). The absolute difference and the relative difference take into account the size of the PBA and are better parameters to judge the predictability of the advancement achieved. The rationale for this unpredictability is largely due to the anatomy of the maxilla and pyriform rims and the adaptation of the PBA to the maxilla. Conclusion: There are distinct advantages to the use of PBA plates. The PBA plates have been proven to significantly affect the advancement. However, when very precise movements are required, the size of the PBA used does not predictably correlate to and frequently underestimates the amount of advancement achieved. Therefore accurate model surgeries are still required for most cases. © 2008 American Association of Oral and Maxillofacial Surgeons.