Assertive Community Treatment (ACT) is a service delivery model designed to provide an integrated approach to care for persons with severe mental illness. The implementation of this model across North Carolina offers an opportunity to study this model at differing levels of fidelity in real-world, uncontrolled settings. We used Medicaid claims files from the years 2000-2002 to look at patterns of emergency room, general medical, primary care, and inpatient psychiatric costs and visits, as well as total costs, using cross-sectional and longitudinal models, including multivariate regression, propensity score analyses and Rosenbaum bounds. ACT significantly decreased inpatient psychiatric and emergency room costs and visits, but increased total costs. These successes were accomplished with what might have been very low or no fidelity ACT teams - and even greater successes at a lower cost were found in higher fidelity teams - and therefore suggest that there is a large potential for ACT to mature in North Carolina into a model that will fully reflect the cost-savings that have been found in ACT teams elsewhere.