Background: Substance abuse is clearly associated with criminal recidivism among offenders with and without mental disorder. Treatment for substance abuse correlates with lower rates of re-offending among participants in outpatient-based as well as institution-based substance abuse treatment programs. However, for offenders with mental disorder, research on the possible preventive effect of substance abuse treatment on criminal recidivism is sparse. This paper reports from on an ongoing naturalistic and prospective interview study on the relationship between post-release outpatient substance abuse treatment and re-offending. Methods: The Stockholm county sample comprises 246 offenders of both genders subjected to a forensic psychiatric assessment, who screened positive for substance abuse problems. Eighty-five percent (n=210) agreed to participate in the study. Baseline data and follow-up interview data, collected immediately on release from incarceration (prison/forensic hospital) and 6 and 12 months later, include self-reported substance abuse, treatment involvement and criminality. By February 2010, data will be available from the first follow-up for 150 participants, from the second follow-up for 80 individuals and from the third follow-up for 10 subjects. Results and conclusions: The focus of the presentation will be recidivism comparisons between substance abuse treatment utilizers and those who decline treatment. Data on ongoing levels of substance abuse, mental health problems and offending will serve as dependent variables. Additional analyses will present perceived benefit from and reasons for accepting or rejecting treatment.