Objective: This study examines the effectiveness of a county jail program for individuals with co-occurring disorders (COD) in reducing rates of recidivism and increasing rates of engagement in community-based treatment following discharge. Methods: Over a period of 30 months, between 2002 and 2004, 261 individuals who screened positive for COD voluntarily entered an in-jail treatment program. The program provided integrated treatment for both mental health and substance abuse by therapists who had attended a state sponsored COD core training curriculum. The same program staff provided outpatient services once individuals were discharged. An observational study design was used to examine jail recidivism and community care as a function of intensity of treatment while in jail. All study participants had a minimum one year follow-up. Data was obtained from a baseline comprehensive screening instrument, administrative claims data and county jail records. Logistic regression models were used to determine the likelihood of re-incarceration and community engagement in treatment as a function of the number of treatment sessions provided by the jail program. Results: County jail records indicated that 47.5% were re-incarcerated within 12 months of discharge. During the four and a half year period following the inception of the COD program 67% were re-incarcerated, which was similar to the national three year recidivism rate. Fifty-two percent (52%) attended a community-based treatment program post discharge. The results of the regression analysis showed that a higher number of treatment sessions in the jail COD program was significant in reducing the rate of re-incarceration but was not significant in predicting who would engage in outpatient treatment post discharge. Conclusions. Although the findings are promising, the evidence suggests that the jail treatment intervention may need to be more intense than the outpatient model used in this project given that the average length of stay in the jail program was 8 weeks due to release to the community. An alternative consideration would be to only provide the program to those inmates who are sentenced for at least 90 days. Copyright © 2009 John Wiley & Sons, Ltd.