Objective: This study examined whether there were differences in costs for mental health court (MHC) participants and a matched comparison group for three years after a target arrest. Methods: Data from the MacArthur Mental Health Court Study, the first multisite study of MHCs, were used to compare behavioral health treatment and criminal justice costs for MHC participants and a matched group (using coarsened exact matching) of jail detainees who were not enrolled in an MHC but who received

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... -based psychiatric services in the same cities. Cost data for three years before and after a target arrest were calculated separately for each year and for each participant at three sites of the multisite study-296 MHC participants and 386 matched jail detainees. High-cost MHC participants were identified. Results: Total annual costs for MHC participants averaged $4,000 more for all three follow-up years. The additional costs resulted from treatment costs, which were not offset by criminal justice cost savings. The highest-cost MHC participants were those with diagnoses of co-occurring substance use disorders and those who had more arrest incarceration days before their target arrest. Separate analyses determined that the higher average costs were not the result of outlier cases. Conclusions: Participation in an MHC may not result in total cost savings in the three years after enrollment. To become more efficient and to serve participants with the greatest needs, MHCs need to more effectively define the target group for intervention.