This review aiming to estimate the overall prevalence of peri-implantitis included 57 studies (18 cross-sectional,18 longitudinal, 17 cohort studies, 3 RCTs and 1 case-control). Meta-analysis found an ooverall patient level prevalence of 20% (95%CI; 16.6 to 23.7%). However most of the studies used convenience samples and there was a marked heterogeneity in the diagnostic criteria used so the findings should be viewed cautiously.