Objective <p>This study aimed to investigate three-dimensional (3D) positional changes of the mandibular condyles following bimaxillary orthognathic surgery performed using the surgery-first approach (SFA) in skeletal Class III patients. The associations between condylar positional changes, other clinical variables, and postsurgical mandibular skeletal relapse were also assessed.</p> Methods <p>Twenty-five adult skeletal Class III patients who underwent bimaxillary orthognathic surgery with the SFA were included retrospectively. Cone-beam computed tomography (CBCT) scans were acquired at three time points: preoperatively (T0), immediately postoperatively (T1), and at 1-year follow-up (T2). 3D translational and rotational condylar displacements, as well as dental and skeletal changes and postoperative stability, were quantified using analysis software. Repeated-measures analysis of variance (ANOVA), Pearson or Spearman correlation tests, and multiple linear regression were used for statistical analysis.</p> Results <p>A significant anterosuperior mandibular relapse was observed at the 1-year follow-up (T2). Immediately after surgery (T1), the condyles showed significant posterior and inferior translational displacement, accompanied by clockwise pitch and medial yaw rotation. While these positional changes tended to return toward their preoperative position by T2, no significant correlation was found between the magnitude or direction of condylar displacement and mandibular skeletal relapse. In contrast, the initial sagittal position and the surgical change in the upper incisors were significant predictors of relapse. Specifically, the initial anteroposterior position accounted for 20.3% of the variance in sagittal mandibular relapse, indicating that greater dental compensation of the upper incisors was associated with increased mandibular relapse. The modest proportion of explained variance suggests that other unmeasured factors also play important roles in postsurgical stability.</p> Conclusions <p>Although postoperative condylar positional changes commonly occur following the SFA in skeletal Class III patients, these changes do not appear to be a primary contributor to mandibular skeletal relapse. Instead, postoperative mandibular stability seems more closely associated with surgical compensatory patterns, particularly upper incisor protrusion. While the SFA demonstrates acceptable skeletal stability, meticulous evaluation and appropriate control of dental decompensation during treatment planning are crucial to minimize postoperative relapse.</p> Trial registration <p>The study was registered at the Chinese Clinical Trial Registry on October 24, 2025 (Identification number: ChiCTR2500111068).</p>