[The practice of systematic reviews. I. Introduction]

A systematic review of the results of randomized, controlled trials employs explicit, systematic methods to produce unbiased and precise estimates of the effect of a treatment on outcomes of clinical importance. The results of such systematic reviews are of importance in that they inform providers and consumers about the effect of treatments and identify priorities for new research. The Cochrane Collaboration is a systematic programme to try to harness this valuable information. An overview of the actual status of systematic reviews of health care interventions is given and a miniseries of papers on systematic reviews is introduced.