Diversion from the criminal justice system to community treatment as a means for reducing the proportion of those incarcerated and affecting criminal justice activity, substance abuse, and mental health disorder stabilization has long been proposed through previous research. This article provides a description of findings from an evaluation of New York City’s NYC-LINK. NYC-LINK is a jail diversion program for those with co-occurring alcohol and/or drug problems and serious mental illness. The study addressed the effect of mandated versus non-mandated diversion, treatment, and individual client characteristics on services access and use, criminal justice rearrests and length of confinement, mental health stability, drug and alcohol use, and life satisfaction. The study was comprised of 231 defendants, both program clients and potential comparison participants. Major findings included that mandated diversion clients were less likely to spend as much time in prison and were more likely to spend time in the community, were linked to treatment, received more treatment, and had decreased drug use. In addition, individual characteristics, treatment, and diversion contributed significantly to the effectiveness of mandated diversion. Tables and references