New technology in newborn screening permits clinicians to approach strategies for defining optimal treatments for newborn-screened conditions. The Health Resources and Services Administration Maternal and Child Health Bureau, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and the Centers for Disease Control and Prevention have all established initiatives for long-term follow-up assessment of children identified after newborn screening. In October 2008, an inaugural meeting of the National Institute of Child Health and Human Development-sponsored National Coordinating Center Long-Term Follow-Up Data Collection Work Group brought together partners from Health Resources and Services Administration-sponsored Regional Genetics Collaboratives to review pilot projects undertaken to promote systematic long-term follow-up for children with inborn errors of metabolism identified by newborn bloodspot screening. Beginning with these projects, the goal of this meeting was to provide a foundation for national planning for a common data set to be used for long-term follow-up. This supplement summarizes these initial projects.