The incidence of mental illness among Colorado’s prison population models nationwide trends. As of June 2005, 16 percent of the Colorado Department of Corrections’ (CDOC) offenders were identified with a serious and pervasive psychiatric disorder. An additional 9 percent were classified as having mental health needs. Altogether, 25 percent of Colorado inmates presented with mental health issues. Among the incarcerated, mental illness was more common among females than males. Although the seriously mentally ill offenders receive the most attention, this study suggests that those who have mental health needs but do not meet strict diagnostic criteria should not be neglected. Effective management and treatment of offenders with mental illness (OMIs) may be costly, but without these, the price paid by prisons and society may be even more costly. The ever present challenge of reducing rising rates of mentally ill persons in the criminal justice system suggests the necessity to learn more about this subgroup of offenders. The present study is exploratory, designed to examine characteristics of OMIs in the Colorado correctional system. Prevalence, release, and recidivism data were investigated to understand the rates of OMIs entering, releasing, and returning to prison. The study profiles mentally ill offenders across demographic, criminal history, psychological, and needs areas as well as some prison adjustment factors to determine how OMIs differ from the general prison population. Tables, figures, references