Objective Cleft lip and palate are the second most common congenital malformations in humans. Secondary alveolar bone grafting (SABG) with autogenous bone is the standard therapy for alveolar cleft defects. However, data regarding postoperative volumetric control of the augmented bone graft are limited. This study aims to evaluate the volumetric outcomes of SABG and to identify potential predictors for the postoperative cleft volume. Methods This retrospective clinical cross-sectional study included 60 patients who underwent SABG between March 2005 and February 2025 at the University Hospital Dresden. Pre- and postoperative cleft volumes were measured using cone-beam computed tomography (CBCT) data and 3D Slicer software. The inter-rater reliability of the volume measurements was assessed using the intraclass correlation coefficient (ICC). The pre- and postoperative volumes were compared using the Wilcoxon test. A linear regression analysis was conducted to identify predictors for the postoperative cleft volume. Results The median preoperative cleft volume was 549.38 mm³ . Postoperatively, the median volume was significantly reduced to 228.75 mm³ (p < 0.001). Patients with pre- and postoperative volume data showed a median volume reduction of 51.4%. The volume measurements showed excellent inter-rater reliability (ICC ≥ 0.997, p < 0.001). The predictor analysis, which included patient demographics, cleft characteristics, and surgical parameters, did not identify any significant predictors for the postoperative cleft volume. Conclusions Secondary alveolar bone grafting with autogenous iliac crest is an effective method for significantly reducing the alveolar cleft defect volume, although considerable bone resorption occurs. Further prospective studies with standardized imaging protocols are needed to better understand the factors influencing graft resorption and long-term outcomes.