[We need fewer but better systematic reviews! A call for action]

Systematic reviews (SR) are an important source for evidence-informed decision-making in the context of health-related questions. Examples of their use include acting as the evidence base for guidelines and health information products, for planning clinical studies, and informing health policy decisions. Accordingly, it is crucial that SR provide trustworthy, reliable summaries of the available evidence. This is why they need to be of high quality in terms of both methods and content. SR suffering from quality deficiencies carry the risk of delivering biased or erroneous and therefore untrustworthy results. For years, the international research literature has highlighted problems with the quantity and quality of SR that undermine their "usefulness", including "mass production" of SR and evidence that a large proportion of all SR is untrustworthy. This poses a considerable challenge to users searching for and selecting suitable SR. In consequence, SR are commonly used uncritically, and health-relevant decisions are made on the basis of biased or erroneous results. This prompts an important question to everyone involved in the production of SR: Why are so many flawed SR being produced and published? The aim of this paper is to point out the importance of SR and the requirements for producing high-quality SR to inform evidence-informed healthcare, to describe the key problems with their quantity and quality, to specify possible reasons for these problems, and to outline approaches to solutions. There is an urgent need for action to make SR "useful" (again).