Over half of the persons with mental illness have substance abuse problems at some point in their lives, and the literature indicates that high rates of substance abuse and mental illness produce behaviors that pose threats to public safety and poor community reintegration outcomes after incarceration. Given the epidemiological data to date, it appears that the dually diagnosed are the majority of offenders rather than a subgroup of offenders. The current study examined offenders with mental illness and those with substance abuse problems (dually diagnosed) in correctional custody across the spectrum of criminal justice settings in Massachusetts. The three levels of criminal justice involvement examined were a preadjudication group, a postadjudication group serving a house-of-correction or misdemeanor sentence that averaged 4 months, and a postadjudication group serving a State prison or felony sentence averaging 4 years. Data were obtained on demographics, clinical symptoms, service needs, criminal history, and outcome (postincarceration functioning after 3 months). The study found that dually diagnosed offenders were more likely to be servicing sentences related to their substance use (public order offenses, property crimes, and drug-dealing offenses) than those with mental illness but without substance dependence. They were also more likely to be homeless upon release, violate probation after release, and recidivate to correctional custody. The double stigma of being a mentally ill substance abuser creates barriers to receiving community-based services. Criminal justice processing for these dually diagnosed individuals does little to help them and in fact their incapacitation separates and stigmatizes them, removing them further from the community. The dually diagnosed have little appreciation for sentences intended to deter them from drug abuse or criminal behavior. Policymakers must find alternative policies for managing the dually diagnosed if their behavior is to be changed through effective treatment. 3 tables, 4 notes, and 45 references