This study reports on a representative sample of prisoners in Michigan correctional facilities to determine the prevalence of psychiatric illness and the delivery of mental health (MH) services. Mental health assessments were conducted with 618 incarcerated subjects using the interRAI Correctional Facilities (interRAI CF). Subjects were randomly sampled based on four strata: males in the general population, males in administrative segregation, males in special units, and females. The interRAI CF assessments were merged with secondary data provided by the Michigan Department of Corrections (MDOC) containing information on MH diagnoses or services that the subjects were receiving within the facilities, demographics, and sentencing. Study results show that 20.1% of men and 24.8% of women in Michigan prisons have a substantial level of MH symptoms and that 16.5% and 28.9%, respectively, are receiving MH services. However, when compared with Michigan Department of Corrections MH care records, 65.0% of prisoners who are experiencing symptoms of mental illness are not currently receiving any psychiatric services. The mis-match between symptoms and service delivery suggests the need for improved procedures for identifying and measuring psychiatric symptoms within Michigan correctional facilities to ensure that appropriate individuals receive needed care. It is recommended that a standardized assessment process be implemented and conducted at regular intervals for targeting and improving psychiatric care in the prison system.