OBJECTIVES: Individuals with a serious mental illness (SMI) often experience recidivistic patterns in the criminal justice system (CJS). It has been argued that the provision of mental health services can disrupt this pattern. We examined the impact of community based mental health services on the arrest patterns of adults with a SMI who became involved in the CJS in Pinellas County Florida and Harris County Texas. METHODS: We identified adults 18-64 years old in Florida and Texas with a SMI who spent at least one day in jail during an index year. Statewide and local administrative data sets were used to document their patterns of arrests and utilization of health and mental health services over 3-4 year periods. Generalized estimating equations were used for count data to estimate the association of outpatient and ER/inpatient mental health contacts in a quarter and arrests in the subsequent quarter. Individual fixed effects models were also estimated to account for unobserved time invariant factors correlated with treatment and the likelihood of arrest. RESULTS: We identified 3769 and 8505 individuals in the Florida and Texas data sets respectively. In Florida, individuals receiving outpatient services in a quarter were 20% less likely to be arrested in the subsequent quarter. The effect was greater for misdemeanor than for felony arrests. Individuals receiving ER/inpatient services were 7% more likely to be arrested in the subsequent quarter, and 13% more likely to have a felony arrest. The association between outpatient mental health services and arrests was confirmed by the individual fixed effects model. Parallel analyses are underway using Texas data to determine if the relationships hold for different jurisdictions and time frames. CONCLUSIONS: Outpatient mental health services were associated with a decrease in the risk of arrests among groups of individuals with a SMI and criminal justice involvements.