A primary goal of health care is to prevent disease or detect it early enough that intervention will be more effective. Strategies for disease screening and prevention are driven by evidence that testing and intervention are practical and effective. Currently, most screening tests are readily available and inexpensive. Examples include tests that are biochemical (e.g., cholesterol, glucose), physiologic (e.g., blood pressure, growth curves), or radiologic (e.g., mammogram, bone densitometry) or that involve tissue specimens (e.g., Pap smear). In the future, it is anticipated that genetic testing will play an increasingly important role in predicting disease risk (Chap. 63). However, such tests are not widely used except for individuals at risk for high-penetrancegenes on the basis of family or ethnic history (e.g., BRCA1, BRCA2). The identification of low-penetrance but high-frequency genes that cause common disorders such as diabetes, hypertension, and macular degeneration offers the possibility of new genetic tests. However, any new screening test, whether based on genetic or other methods, must be subjected to rigorous evaluation of its sensitivity, specificity, impact on disease, and cost-effectiveness. Physicians and patients are introduced continually to new screening tests, often in advance of complete evaluation. For example, the use of whole-body CT imaging has been advocated as a means to screen for a variety of disorders. Though it is appealing in concept, there is currently no evidence to justify this approach, which is associated with high cost and a substantial risk of false-positive results.