[The systematic review is the foundation of evidence based medicine. One of the most important contributions to clinical medicine of the past decade].

The traditional narrative review has been shown repeatedly to be biased, mostly towards exaggerated treatment size effects. In contrast, the systematic review follows a strict protocol regarding focused questions, explicit criteria for literature searches, inclusion and exclusion criteria, critical appraisal and a synthesis which is quantitative when appropriate. There is empirical evidence that bias is reduced and that the conclusions reached have greater validity for the construction of treatment guidelines. In this paper three sources of systematic reviews are identified: the Cochrane Library, reviews published in peer-reviewed journals, and assessments of health technology (HTA-reports). Editors are encouraged to publish systematic reviews after proper critical appraisal, and readers are advised to search for such reviews when in need of guidance on important clinical questions.