The jail-involved population-people with a history of arrest in the previous year-has high rates of illness, which leads to high costs for society. A significant percentage of jail-involved people are estimated to become newly eligible for coverage through the Affordable Care Act's expansion of Medicaid, including coverage of substance abuse treatment and mental health care. In this article we explore the need to break down the current policy silos between health care and criminal justice, to benefit both sectors and reduce unnecessary costs resulting from lack of coordination. To draw attention to the hidden costs of the current system, we review three case studies, from Washington State, Los Angeles County in California, and New York City. Each case study addresses different aspects of care needed by or provided to the jail-involved population, including mental health and substance abuse, emergency care, and coordination of care transitions. Ultimately, bending the cost curve for health care and criminal justice will require greater integration of the two systems.