The aim of this retrospective study was to evaluate long-term clinical and radiologic outcomes of submerged and nonsubmerged guided bone regenerative treatments for peri-implantitis lesions. Strict methods of implant-surface decontamination and detoxification were performed. Data on clinical probing depth, soft tissue measures, and marginal bone level that were documented by comparative radiographs were obtained from 45 patients, for a total of 57 implants prior to treatment and at the latest follow-up. The average follow-up period was 6.9 years (range: 2 to 21 years). Analysis of implant-based data revealed a success rate of 70.2% for a total of 40 implants. Recurrence of peri-implantitis was observed on 9 implants, and 8 implants were removed. The regenerative procedures, under a strict periodontal control, were effective in the treatment of moderate to advanced peri-implantitis lesions.