The objective of this paper was to evaluate the current evidence reporting on the prevalence of peri-implantitis and to determine the influencing factors. An electronic search for articles published until February 2019 reporting on the prevalence of peri-implantitis was performed in MEDLINE. Included criteria were published in international peer-reviewed journals, written in English language, reported on the prevalence of peri-implantitis, included implants with a minimum follow-up of one year after functional loading and used a clear definition for peri-implantitis and/or peri-implant mucositis with a clear cutoff for bone level changes according to the case definitions of Sanz and Chapple and Berglundh et al. 2018. Included papers were anaylized for factors affecting the reported prevalences for peri-implantitis. Twenty-five papers were included in the present review and a wide range for the reported prevalence of peri-implantitis was seen. Case definitions for peri-implantitis with various thresholds for bone loss together with the type of reporting on patient- or implant-level were the most significant factors that lead to a large variety of the occurrence of the disease. Additionally, follow-up time and the evaluation in a certain "convenience" population may have influenced the prevalence values. In conclusion, it can be stated that a wide range for reporting the prevalence of peri-implantitis can be found and no real estimation of the global burden of the disease can be made. Applying accurate case definitions for peri-implantitis is the most important factor for reporting the prevalence and should be strictly followed in future reports.