Screening for cancer is an important focus of cancer control. Yet screening, as it involves administering a test to large segments of the population deemed to be at risk for the disease of interest, is potentially a major consumer of scarce health care resources. In addition, the benefits sought from cancer screening, particularly reduction in mortality from the disease, are not always realized, either for biological or organizational reasons. Thus, the paradigm that "early detection must always be beneficial", taught to health care professionals, and publicized widely through the media to the public, has been challenged in the last two decades for a number of cancer sites. It is the purpose of this text to determine the extent to which the requirements for the introduction of population-based screening programmes have been met, as a result of extensive research on screening during the last two decades, with a major concentration on findings from the recent decade.
