New testing methodologies permit a rapidly expanding menu of screening techniques for genetic diseases in the prenatal, newborn, and adult populations. Tandem mass spectroscopy has markedly increased the number of genetic disorders that potentially can be incorporated into newborn screening. Adult carrier screening is discussed in detail for cystic fibrosis, hemachromatosis, hemoglobinopathies, and other disorders. A review is provided of the relevant criteria for selecting diseases to be screened, the limitations of genetic tests that address only a component of the overall mutation spectrum for a given disease, and related educational and informed consent issues. © 2006 John Wiley & Sons, Inc.