Bone regeneration and reosseointegration around a dental implant were radiographically and histologically analyzed after regenerative treatment for peri-implantitis, using a case from a human autopsy. A block specimen including the tissue around the implants was obtained from the patient, who died from cancer 20 months after regenerative surgery using a synthetic bone substitute to treat peri-implantitis. Microcomputed tomographic and histologic analyses were performed. Three-wall intrabony defects at the implant placed at the site of the mandibular left first molar and a circumferential defect at the implant at the site of the mandibular left second molar were substantially filled with newly formed bone and residual bone substitute particles, and reosseointegration on the previously exposed implant surface was histologically observed.