Seventy-eight inmates (75 percent) were diagnosed with severe mental illness. Of these 78 inmates, 59 (76 percent) required inpatient care or its equivalent for part of their stay in jail for their current offense. Of the inmates with severe mental illness, 92 percent had a history of failure to take their prescribed medications prior to the current arrest; 95 percent had prior arrests; 72 percent had prior arrests for violent crimes against persons; and 76 percent had a history of substance abuse. These findings show that a large percentage of the individuals with severe mental illness received acute psychiatric inpatient treatment while in the care of the criminal justice system rather than from the community mental health system. The severely mentally ill individuals in this study would present a major challenge for the provision of treatment in any setting, given their psychiatric and criminal histories. The resources of the mental health system should be greatly expanded in order to meet this challenge, with priority given to treatment for persons who have engaged in criminal behaviors or who have symptoms that place them at risk for criminal behaviors. The study obtained data on the demographic characteristics, diagnoses, psychiatric and legal histories, and current psychiatric conditions and treatment for a random sample of 104 male inmates with mental illness. Data were obtained from jail psychiatric records, the electronic county mental health records, and State records of criminal histories. 3 tables and 18 references