Findings from the study suggest that 15.2 percent of newly committed offenders at low-, medium-, and high-security facilities may require some level of mental health services to address a need related to mental illness. Prevalence rates differed between gender and between lower versus medium or high security levels. The study discussed implications which inform the work of clinicians, administrators, and policymakers. Future research was recommended in the development of additive models estimating service need among other components of corrections populations. From the moment of their admission to prison, offenders with mental illness represent a population with special service needs. From this service perspective, this study drew population estimates of mental illness indicators for newly committed offenders. It examined multiple sources of data on a contemporary, nationally representative group of 2,855 male and female Federal offenders across 3 security levels and 5 regions of the United States. Tables, notes, and references