The Cochrane Collaboration is a large international organization engaged in the production and maintenance of systematic reviews of results of randomized controlled trials in all areas of health care. Reviewers are supported by 50 Cochrane Collaborative Review Groups based around the world. Reviews are published in The Cochrane Database of Systematic Reviews (CDSR), and various other publications provide a central register and database and a methodology register. Currently, over 4000 reviews have been undertaken, with results now available from 2000.