Aim: Present a clinical case regarding surgical treatment of a peri-implantitis severe defect with a xenograft/L-PRF block. Clinical Case Presentation: A healthy non-smooker patient, presented peri-implantitis on implant #14 (NobelReplace, 4.3x13, Nobelbiocare, Switzerland) (PD= 7.17±0.98mm + BOP (DB+DP) and radiographic bone loss (4.4±0.8mm)). Venipuncture was performed to prepare L-PRF membranes (Choukroun et al. 2001). A mucoperiosteal flap exposed a peri-implant Cl Id defect. Implant surface was decontaminated with a titanium curette and glycine air-flow. A L-PRF/xenograft (Creos xenogain, NobelBiocare) block was prepared, applied to the defect and coved with L-PRF membranes. Flap was sutured (polypropylene 5/0) and implant left submerged. Results: About 9 months later standardized radiographs were taken and practically complete intra-bony defect resolution achieved (0.53±0.74mm) as well as some supra-bony defect fill. Clinically the PD was 3.33±0.52mm. Discussion: Peri-implantitis regenerative surgical treatment still needs further investigation (Schwarz et al. 2015). An effective decontamination that not causes implant surface alterations is crucial for success and glycine air-flow presents those characteristics (Schwarz et al., 2016, Sahrmann et al., 2015). Xenograft resulted in favorable results in less demanding defects (Schwarz et al., 2006) and L-PRF already demonstrated an healing ability in periodontology (Castro et al., 2017). The L-PRF/xenograft block allowed a higher biomaterial stability and allows it's application on more demanding peri-implant defects. Other authors, in different PI defects, had a PD decrease with only L PRF (Hamzacebietal.2015). Our radiographic results demonstrated a peri-implant bone gain in major PI defects. Conclusions: This clinical case presented the clinical and radiographic resolution of a more biological demanding peri-implant defect. Keywords: Peri-implantitis, Surgical treatment, leucocyte platelet rich fibrin (L-PRF), xenograft