Aims of Procedures: We intend to present a technique of reconstruction of maxillary horizontal bone defects by applying, fresh-frozen cortico-cancellous blocks allografts, from the Bone Bank, Faculty of Medicine, University of Coimbra, in the onlay technique, with the aim of implant supported prosthetic rehabilitation. Case Report: A 46-year-old female with lack of retention of the upper denture. After careful review intraoral and initially, under local anesthesia, proceeded to the exposure of the alveolar crest. The blocks were prepared, stabilized and fixed to the native bed using micro-screws. After five months, reopened to remove the screws and eight implants were placed. Six months later, the patient received an implant supported rehabilitation. Results: During the re-entry procedures, all the blocks were found to be firm in consistency, well-incorporated and vascularized, with minimal resorption, allowing the installation of eight implants. There were no post-operative complications. After twelve months, the implant-supported rehabilitation was in perfect function and none of the implants were lost. Discussion: The reconstruction with onlay bone blocks, provides better outline and resistance to implant placement. The application of fresh-frozen bone blocks allografts allowed good adaptation to the recipient site, reduced operative time, less morbidity, greater availability, security implementation and patient comfort compared to the application of autografts. Conclusion: Bone reconstruction by the application of fresh-frozen allogeneic bone blocks under local anesthesia by applying the onlay technique has been shown to be a suitable alternative to the use of autografts, in bone reconstructions at a short period of time. Schlagwörter: Bone blocks, onlay technique, bone allografts, cortico-cancellous, horizontal bone defects, recipient site.