Newborn screening for metabolic, hematologic, and endocrinologic disorders is a well-established public health function. Recent technological advances have made screening possible for more disorders. For many of these disorders, there is evidence that screening is effective; however, some of these disorders are rare, and their response to therapy and their natural history are not completely understood. A number of states have instituted "expanded" newborn screening utilizing a combination of established and new technologies. Other states, including Delaware, have studied the experiences of the states doing expanded screening and have decided to proceed with expanded screening as well. Since early 2003, Delaware has been screening newborns for about 25 disorders, including amino acidopathies, organic acidurias, fatty acid oxidation disorders, hemoglobinopathies, and endocrinopathies.