The province of Ontario, Canada, with a population of 13 million people, has a large Assertive Community Treatment (ACT) program. Despite the large uptake of ACT in Ontario, to date there has been no comprehensive evaluation of the degree to which the model has been successfully implemented. This project assessed the fidelity of 67 ACT teams (85%) in the province using the Dartmouth Assertive Community Treatment Scale. Scores fell in the high fidelity range in the human resources and organizational boundaries domains, and in the medium fidelity range for the nature of services domain. Areas requiring more attention include achievement of higher caseloads; recruitment and retention of staff (specifically vocational, substance abuse, and psychiatry staff); and key areas of recovery, specifically employment and substance abuse.