The objective of this study is to determine the reduction in inpatient psychiatric recidivism and costs associated with an intensive case management (ICM) program among high-risk adults with chronic mental health conditions. An intent-to-treat, historical control design was used to examine utilization differences between 306 intervention group (IG) members eligible to receive ICM services and a cohort of 290 baseline group (BG) members over a six-month outcome period. Members were identified retrospectively using identical criteria during one year prior to implementation of the program. The six-month recidivism rate for BG members was 49.67% compared to 22.07% among IG members. Forward stepwise regression results indicated a significant main effect for the ICM intervention on inpatient psychiatric costs. Inpatient psychiatric costs for the six-month outcome period were $4,982.90 lower per member in the IG group. Additional models demonstrated that the ICM intervention was associated with significantly lower inpatient substance abuse costs and psychiatric emergency department costs. There were no statistically significant increases in utilization associated with the ICM intervention. After factoring in program costs, it is estimated that the ICM services contributed to almost $1,500,000 in cost savings over the six-month outcome period. The ICM intervention was associated with significant reductions in inpatient, psychiatric six-month readmission rates and associated costs among adult members who are at elevated risk of inpatient, psychiatric recidivism. The intervention, enrollment process, and measurement strategies can be adapted for use by health plans looking to reduce psychiatric costs.