This report from the Washington State Institute for Public Policy presents the results of a study that examined the cost-effectiveness and impact on recidivism rates resulting from the State's Dangerous Mentally Ill Offender (DMIO) program. The program was established by the State legislature in 1999 to identify mentally ill prisoners who pose a threat to public safety and provide them with opportunities to receive mental health treatment and other services up to 5 years after their release from prison. This study evaluated the outcomes for 172 DMIO designees who were released from prison during the first 3 years of program implementation and compared them to individuals with similar characteristics who did not participate in the program. The evaluation found that offenders who participated in the DMIO program were significantly less likely to commit any new felony, were less likely to be reconvicted of a new felony, and less likely to commit a new violent felony. In addition, the cost/benefit analysis indicated that the decrease in criminal recidivism attributed to the DMIO program resulted in a net economic benefit to crime victims and taxpayers coming primarily from a reduction in criminal justice system expenditures. This evaluation reinforces the findings from previous studies that have identified a net benefit to the DMIO program. 3 exhibits