Patterns of mental health (MH) and substance abuse (SA) treatment utilization among populations receiving services through multiple public programs are not well known. This study examines to what extent populations with MH and/or SA conditions utilize treatment services through Medicaid and State MH/SA Agencies. Data are from the Substance Abuse and Mental Health Services Administration Integrated Database, a multiyear file for 3 states combining Medicaid and State MH/SA Agency administrative data into a uniform database. Although populations with co-occurring conditions and those served by both Medicaid and State MH/SA Agencies have substantial contact with the public treatment system, a majority of the MH/SA populations examined here utilize few services over brief periods of time. Utilization is most limited among individuals with MH-only conditions and those served exclusively by Medicaid. While a lack of data on clinical outcomes prevents us from drawing conclusions about the effectiveness of MH/SA services, results of this analysis indicate that public programs in the states examined here do not provide services that are primarily utilized on a frequent or chronic basis.