P>Objectives To evaluate the extent of bone fill over 3 years following the surgical treatment of peri-implantitis with bone grafting with or without a membrane. Material and Methods In a non-submerged wound-healing mode, 15 subjects with 27 implants were treated with a bone substitute (Algipore (R)) alone and 17 subjects with 29 implants were treated with the bone substitute and a resorbable membrane (Osseoquest (R)). Implants with radiographic bone loss >= 1.8 mm following the first year in function and with bleeding and/or pus on probing were included. Following surgery, subjects were given systemic antibiotics (10 days) and rinsed with chlorhexidine. After initial healing, the subjects were enrolled in a strict maintenance programme. Results Statistical analysis failed to demonstrate changes in bone fill between 1 and 3 years both between and within procedure groups. The mean defect fill at 3 years was 1.3 +/- (SD) 1.3 mm if treated with the bone substitute alone and 1.6 +/- (SD) 1.2 mm if treated with an adjunct resorbable membrane, (p=0.40). The plaque index decreased from approximately 40-10%, remaining stable during the following 2 years. Conclusion Defect fill using a bone substitute with or without a membrane technique in the treatment of peri-implantitis can be maintained over 3 years.