In recent decades, a decline in caries has led to retention of more teeth in industrialised countries. However, it is unknown, if such a trend also exists for periodontitis. Thus, the aim of this article is to review the evidence for global trends in the change in the prevalence of periodontitis over the last 20 years. Because evaluations of disease trends and comparisons of those between-trend studies are complicated by several methodological aspects, we also comprehensively discuss these issues. In total, ten studies provided data on trends in periodontal diseases with varying degrees of methodological bias. All studies consistently reported declining trends of periodontal parameters. However, methodological issues partly restricted interpretability of trend studies. Nevertheless, this review supports the assumption that periodontal disease prevalence is declining, though to varying degrees, but we will probably face higher treatment demands in the future because the number of teeth within subjects as well the number of elderly subjects within populations is increasing.