Rapid advances in the field of human genetics have led to an increase in the availability of genetic diagnostic tests. This article reviews technical approaches and diseases for which metabolic, newborn screening, molecular, and cytogenetic diagnostic tests are available currently. Overlaps in areas of diagnostic testing that have emerged from the application of new technology in the field of genetics also are discussed, as are criteria and approaches used for identifying conditions for which diagnostic, presymptomatic, prenatal, and carrier testing should be offered. Finally, the delivery of these results and necessary genetic counseling that should accompany this information are reviewed.