AimTo determine the prevalence and development of peri-implant mucositis and peri-implantitis and to assess risk factors over time. Materials and MethodsThe study is a longitudinal case series assessing the occurrence and diagnosis of peri-implant mucositis and peri-implantitis. ResultsA total of 218 of 294 patients who had received dental implants between 1988 and 1992 were examined between 2000 and 2002 (examination II; 9-14years after the first examination). At examination III (20-26years after examination I, on average 23.3years), 86 individuals were re-examined. The diagnosis of peri-implant mucositis and peri-implantitis at examination III was 54.7% and 22.1%, respectively. Surgical treatment of peri-implantitis after examination II resulted in a bone gain for two of 12 individuals. Individuals with 3 implants at examination II were at risk for peri-implantitis at examination III (P< 0.05). Radiographic evidence of periodontitis (p=0.40), a diagnosis of peri-implant mucositis (p=.77) or smoking (p=.86) at examination II were not predictive of peri-implantitis at examination III. ConclusionsThe diagnosis and occurrence of peri-implantitis and peri-implant mucositis were high. Healthy conditions at implants after 9-14years were predictive of future implant health.