Deinstitutionalization of large institutions for individuals with mental retardation has been an ongoing process for almost 20 years. Because the process continues and because there are still many concerns about deinstitutionalization, especially for populations with more challenging behaviors, the question of relative costs of institutional services and community services is raised periodically by legislators, bureaucrats, and advocates. This study compares the costs within one institution, Fairview, in Oregon, with the costs of providing community-based services in five small group homes and an apartment complex serving populations with more challenging behaviors. In general, institutional costs are slightly higher than the community-based programs. However, after equalizing salary rates between the two environments, community-based residences that serve individuals with challenging behaviors are more expensive than the institution.Deinstitutionalization of large institutions for individuals with mental retardation has been an ongoing process for almost 20 years. Because the process continues, and because there are still many concerns about deinstitutionalization, especially for populations with more challenging behaviors, the question of relative costs of institutional services and community services is raised periodically by legislators, bureaucrats, and advocates.This study compares the costs within one institution in Oregon-Fairview Hospital and Training Center (Fairview)-with the costs of providing community-based services for populations with challenging behaviors. The costs of five residential facilities in various communities in Oregon are examined to compare costs with Fairview and to provide information about costs of residential services to certain groups of persons with challenging behaviors. We analyse these cost data using an analytical framework designed to show not only where cost differences occur, but why.Our framework is fairly simple, yet provides for powerful differentiation in why costs differ across sites and between institutions and community-based group homes. The central premise of our framework is that need determines