Aim: to compare the outcome of allogenic bone sheets clinically and radiographically in posterior mandibular vertical augmentation in Luhr class III cases with simultaneous implant placement using autogenous versus xenografts. Patients and methods: this study was based on a total of 12 implants placed in 4 patients, 2 of which were males and 2 females. Patients were divided into 2 groups, both treated with implants placed with exposed threads 3 mm crestally and covered buccolingually with the laminar bone membrane; group 1 received autogenous bone obtained from the same surgical site using 4.5 diameter ACM bur mixed with PRP and packed around the crestally exposed implant threads. Group 2 received xenograft bone particles mixed with PRP and packed around the crestally exposed implant threads in the same manner. Results: CBCT was done pre-operatively, immediate post-operatively and 4 months post-operatively for each implant to compare the bone gain radiographically. In group 1, the mean amount of residual bone height pre-operatively was 7.8 mm (SD 0.86) and increased to 14.44 mm (SD 1.75) and 14.1 mm (SD 1.85) immediate and 4 months post-operatively, respectively. The mean amount of bone gain after 4 months was 6.3 mm, denoting a minimal amount of graft loss during the first 4 postoperative months was 0.27 mm (less than 2%). In group 2, the mean amount of residual bone height pre-operatively was 8.37 mm (SD 0.99) and increased to 12.86 mm (SD 1.75) and 12.53 mm (SD 1.65) immediate and 4 months post-operatively, respectively. The mean amount of bone gain after 4 months was 4.16 mm, denoting a minimal amount of graft loss during the first 4 postoperative months was 0.33 mm (less than 3%). Upon comparing bone gain in both groups, Group I (Autogenous) had a bone gain of 6.33 mm versus 4.16 mm for Group II (Xenograft). Denoting more gain in Group I (autogenous). While the amount of graft loss between the immediate and 4 months postoperative CBCT was less than 2% and less than 3% in the autogenous versus the xenograft group respectively. Conclusion: Cases initially lacking keratinized mucosa will need soft tissue intervention along with this technique. Exposure after 4 months appeared to have been too early, which lead to bone loss and exposed threads. Bilateral augmentation has led to patients using the grafted edentulous sites for mastication early following soft tissue healing, prior to prosthetics, which might suggest that tooth-bounded posterior edentulous sites might be a better candidate for such technique. Results were clinically different than radiographically in the CBCT, so longer lag time is recommended before loading.