AbtractBackground The process of systematically reviewing research evidence is useful for collecting, assessing and summarizing results from multiple studies planned to answer the same clinical question. The term ''systematic'' implies that the process, besides being organized and complete, is transparent and fully reported to allow other independent researchers to replicate the results, and therefore come to the same conclusions. Hundreds of new systematic reviews are indexed every year. The growing number increases the likelihood of finding multiple and discordant results. Objectives To clarify the impact of multiple and discordant systematic reviews, we designed a program aimed at finding out: (a) how often different systematic reviews are done on the same subject; (b) how often different systematic reviews on the same topic give different results or conclusions; (c) which methods or interpretation