These newborn screening fact sheets were developed by the Committee on Genetics of the American Academy of Pediatrics with considerable assistance and consultation from many individuals. The fact sheets were not designed to advocate specific newborn screening tests but rather to inform pediatricians about these tests. Many states are considering addition of new tests to their screening batteries, whereas others may be reviewing their current screening panel to reduce the number of disorders for which tests are offered. This information should assist pediatricians in developing appropriate positions based on the needs of their patients and of their geographic regions. In addition, the information in these fact sheets may assist the pediatrician in understanding the individual tests, their characteristics, and their strengths and weaknesses. Such information is important for evaluating policies and procedures. Our knowledge base regarding newborn screening is changing rapidly and there are numerous areas of controversy. We have attempted to provide a consensus viewpoint, but it must be recognized that experts in this field do not always agree. Pediatricians who desire additional information should contact the specialists in their region or those involved at a national level. Brief bibliographies have been provided to assist the clarification of some of these points. These fact sheets will require revision in the future. Your comments and suggestions will be appreciated. NOTE ON COST: The costs quoted here are those for the screening tests in a regionalized laboratory. There is a program cost of approximately $1 to $2 for specimen handling, administration, equipment depreciation, and overhead that has been traditionally ascribed to phenylketonuria.