Purpose: The aim of this study was to investigate bone formation over time following maxillary sinus augmentation with an enzyme-deantigenic, bone collagen-preserving equine bone graft by retrospective assessment of histomorphometric data. Materials and Methods: Records of patients with atrophic ridges who underwent maxillary sinus augmentation with the enzyme-deantigenic equine bone graft and two-step implant placement between 3 and 12 months after the sinus-augmentation surgery were assessed retrospectively. The histomorphometric data were clustered in three classes according to time of collection from the augmentation surgery and analyzed to assess newly formed bone deposition and residual biomaterial degradation rates. Data concerning the 36-month clinical follow-up were also assessed. Results: Records of 77 patients and 115 biopsy specimens were retrieved, and histomorphometric data were clustered (3 to 5 months, n = 33; 6 to 8 months, n = 57; 9 to 12 months, n = 25). Mean minimum atrophic ridge thickness was 4.9 ± 0.5 mm (range, 4.0 to 7.1 mm). The amount of newly formed bone and residual biomaterial did not significantly differ among the three clusters. Qualitative analysis showed a denser trabecular structure in late (> 8 months) samples. At the 36-month clinical follow-up, no differences were found among the implant success rates in the three groups, according to the Albrektsson and Zarb criteria for success. The overall implant success rate was 98.3%. Conclusion: Based upon this retrospective human study of 77 patients with 4 to 7 mm of residual bone, when enzyme-deantigenic equine bone is used for sinus augmentation, new bone formation occurs at an early time ( 3 months) after the grafting, and implant placement can be safely carried out as soon as 3 to 5 months after the augmentation surgery. Keywords: biomaterial, bone remodeling, sinus augmentation, xenograft