Clinicians have long relied upon diagnostic tests for 'evidence' of the presence or absence of a disease or a condition. Similarly, policy makers must evaluate the value of a particular diagnostic test, compare it to any others, and decide which test should be made available or funded. Methods to synthesize evidence from diagnostic test accuracy studies are now emerging and this text examines the methodological basis to the synthesis of diagnostic test accuracy data and describes the processes involved in the conduct of a diagnostic test accuracy systematic review. Although screening studies share some similarities with diagnostic studies and may report similar statistics, screening is typically applied to uncover very early signs of disease or the risk of disease, whereas diagnostic tests are generally applied to individuals with signs or symptoms of disease. Issues of meta-analysis of screening studies are discussed elsewhere.