The number of mentally ill offenders in prison rose dramatically between 1980 and 1990, in part because of a drop in the number of long-term psychiatric beds, decreasing community support, and rigid criteria for civil commitment. In addition, certain characteristics prevalent among mentally ill individuals increase the likelihood of incarceration, including use of illicit drugs, failure to continue in treatment, and violent behavior. For this study, 109 male offenders were interviewed, volunteers from among inmates at the Washington State Corrections Reception Center. Of the 96 mentally ill offenders, 64 had a diagnosis other than a substance abuse disorder, and of these offenders, 54 also had a diagnosis of alcohol abuse or dependence or drug abuse or dependence. Previous studies have found that drugs and alcohol are available in prison and it is almost impossible for a chemically addicted mentally ill person to maintain sobriety in such an environment. Further attention is needed to substance abuse as a contributor to incarceration of the mentally ill and substance abuse should be addressed in community-based mental health programs that provide services to former prison inmates who are mentally ill. Table, references