The novel long-acting injection of risperidone, administered once every two weeks, is the first long-acting formulation of an atypical antipsychotic. OBJECTIVE: To document the hospitalization rates in stable patients with schizophrenia or schizoaffective disorder during long-term treatment with intramuscular injections of long-acting risperidone (25 mg or 50 mg). METHODS: Hospitalization information over the past 3 month period was collected at baseline and every 3 months thereafter as part of a resource use assessment alongside a 1 year multi-center, open-label study in patients with schizophrenia or schizoaffective disorder. RESULTS: Of 397 patients included in the analysis, 301 (76%) were outpatients, while 96 (24%) were hospitalized inpatients at baseline. The need for hospitalization decreased continuously over time during treatment with long-acting risperidone from 38% (150/397) during the 3 months prior to study entry to 28% (111/396) during months 1-3, 18% (64/359) during months 4-6, 14% (42/303) during months 7-9 and 12% (33/281) during months 10-12. This trend over time was statistically significant (p<0.0001; longitudinal data analysis using generalized estimating equations). As a proxy measure for relapse, the 1 year re-hospitalization rate was defined as the first hospitalization for outpatients and a new hospitalization after discharge for inpatients at baseline. Of the inpatients at baseline, 28 patients were not discharged during the study period and did not contribute to the re-hospitalization analysis. The overall 1 year re-hospitalization rate was 17.6% (65/369). In outpatients, the hospitalization rate was 15.9% (48/301), while in inpatients, the re-hospitalization rate was 25.0% (17/68). CONCLUSION: The need for hospitalization decreased continuously and significantly over a 1 year period of treatment with long-acting risperidone. The 1 year re-hospitalization rate associated with long-acting risperidone was low at 17.6%.