Purpose: Treatment of the posterior atrophic mandible has long been a challenge in implant dentistry and maxillofacial surgery. The objective of this study was to reevaluate the safety and efficacy of the sandwich osteotomy and bone grafting in patients with moderate to severe posterior mandibular atrophy. Materials and Methods: This retrospective study included patients with an edentulous posterior mandible in which there was not enough bone above the dental nerve to insert implants at least 10 mm in length; patients with adequate bone volume but with an excessive interocclusal distance at the posterior occlusal region were also included. Twenty-three patients with 30 sites of moderate to severe posterior atrophy were treated using a sandwich osteotomy above the mental nerve and an interpositioned block of autologous or allogeneic bone. Success criteria were based on the possibility of implant insertion after bone grafting. Results: The average gain in height was 5.3 mm (range, 2 to 10 mm). Partial loss of alveolar height was observed in only one patient from the allogeneic graft group. Patients were followed for 12 to 93 months after bone grafting. No signs of infection were observed. Minor dehiscence of the surgical wound occurred in four segments, but healing ultimately occurred in every patient. Sixty-five implants were placed, and none were lost during follow-up. Insertion of implants of 10 mm or more in length was successfully achieved in 90.8% of the sites, and partial success (ie, bone segments suitable for insertion of shorter implants) was seen in the remaining sites. Conclusions: Moderate to severe posterior mandibular atrophy can be successfully treated by interpositional sandwich osteotomy and bone grafting, allowing for the subsequent placement of implants and fixed prostheses in all segments. Keywords: atrophic mandible, dental implants, inlay bone grafting, sandwich osteotomy