The study sought to estimate the number of programs in the U.S. for severely mentally ill adults that used the assertive community treatment model and to describe variations in characteristics of the intervention across programs.Assertive community treatment programs identified by state mental health authorities completed a 12-item survey. The survey included questions on caseload, composition of the treatment team, nature of services, and structure of service provision.A total of 303 of 340 programs (89 percent) identified by states responded to the survey. More than 75 percent provided most of their services in the field, delivered medications, included medical staff on the assertive community treatment team, and had caseload ratios of less than 20 consumers for each provider.Assertive community treatment programs have disseminated quite unevenly across 33 states, with the highest concentrations of programs in midwestern and eastern states.