This report summarizes recommendations that were developed to establish a more consistent approach to operationalizing the case definition for the purpose of public health surveillance among adults with intellectual disability in the United States. The approach included consideration of well established conceptual definitions, such as in the International Classification of Disability, Health, and Function (ICF), and the most recent version of the definition established by the American Association on Intellectual Disability (AAIDD). Additionally, the definitions used in current national and state level major data collection efforts, as well as those used in targeted research studies were considered, with a recognition that these sources are likely to remain the foundation upon which a national surveillance system will be built, and that any recommended definition must accommodate or ‘fit over’ those used in current data collection.