OBJECTIVES: Non-adherence to antipsychotic therapy can lead to increased risks of relapse and rehospitalization.  Long-acting injectable antipsychotics have been shown to be effective and well-tolerated, with increasing evidence of a potential benefit on adherence.  At the time of this study, only one long-acting injectable atypical antipsychotic entity – risperidone - was approved for patients with a diagnosis of schizophrenia.  The objective of this study was to determine the medication adherence rates of Medicaid patients treated with either 1) oral risperidone only, or 2) long-acting injectable risperidone +/- oral risperidone. METHODS: Texas Medicaid prescription claims data from January 2006 to December 2008 were analyzed for patients with schizophrenia. Records were assessed for a period of 18 months (6-month pre-index period with no antipsychotics plus 12-month post-index period).  A medication possession (MPR) ratio of ≥ 80% was considered adherent. RESULTS: A total of 1313 patients met inclusion criteria, and less than half, 48% (N = 626) had an MPR of at least 80%.   Of the patients on long-acting injectables +/- oral risperidone, 60% (N=96/160) were adherent with their regimen versus 46% (530/1153) for patients taking only oral risperidone.  A logistic regression analysis adjusting for demographic covariates (gender, race, age) showed that patients on injectable +/- oral medications were about 80 percent more likely to be adherent (OR=1.82, 95% CI = 1.29-2.55; p=0.0006) than patients on oral medication alone.  There were no statistically significant differences in any of the demographic characteristics between the two groups. CONCLUSIONS: Overall, about half of the patients did not meet the definition for medication adherence (MPR ≥ 80%) one-year after their index date.  Long-acting injectable risperidone had a higher rate of adherence compared to oral risperidone alone.  With the release of newer atypical long-acting injections (paliperidone and olanzapine), future studies comparing adherence rates of these antipsychotic agents are needed.