Purpose: To compare volumetric changes after sinus augmentation of completely edentulous maxillae with either autogenous or allogeneic fresh-frozen bone particles. Materials and Methods: This split-mouth study in patients who required bilateral sinus grafting used autograft particles for one sinus and allograft particles for the contralateral sinus. The grafted sinuses were left to heal for 6 months prior to implant insertion. All patients underwent four computed tomography scans: prior to augmentation and 1 week, 6 months, and 12 months after grafting. Computer software was used to analyze bone graft volume in each scan. Results: Fifteen patients (8 men, 7 women) with a mean age of 54 ± 5 years (range, 48 to 60 years) took part and underwent 30 sinus augmentation procedures. Mean autograft and allograft volumes were not statistically significantly different at each time point (1 week: 2.01 ± 0.43 cm3 vs 2.46 ± 0.79 cm3; 6 months: 1.53 ± 0.49 cm3 vs 1.75 ± 0.64 cm3; and 12 months: 1.38 ± 0.43 cm3 vs 1.59 ± 0.56 cm3, respectively). Mean volumetric reductions of 31.35% and 35.36% (23.9% and 29.9% in the 6 months prior to implant insertion, followed by an additional 9% and 9% in the following 6 months), relative to 1 week postgrafting, were noted for the autograft and allograft groups, respectively, after 12 months. Conclusion: On the basis of this split-mouth study of 15 patients, there was no statistically significant volumetric difference after 12 months between the use of autograft or allografts for sinus augmentation. Fresh-frozen bone allograft may serve as an alternative that avoids the morbidity associated with autograft harvesting. Schlagwörter: autogenous bone, computed tomography, fresh-frozen bone allograft, sinus augmentation