The purpose of this study is to assess the effectiveness and safety of long-acting risperidone given as a once monthly injection to adult patients with schizophrenia or schizoaffective disorder.

Risperidone, taken by mouth on a daily basis, has been an effective treatment for schizophrenia and schizoaffective disorder. Risperidone is also available in a long-acting injectable form so that patients can take their medicine by bi-weekly injections. This study will assess the effectiveness and safety of long-acting risperidone injection given once a month instead of every two weeks (based on previous studies with dosing every 2 weeks). During the four-week lead-in phase, patients will receive one 50-milligram injection every two weeks for two doses. Patients continue to take their prescribed dose of risperidone tablets (from 2 to 6 milligrams per day) for the first 14 days. After the first month, patients will receive one 50-milligram injection once a month for 48 weeks. This dose can be increased to 75 milligrams if patient meets relapse criteria, and is willing to stay in the trial. Patients will be asked questions to help determine how well the monthly injections are working. Laboratory tests (including drug levels), physical examinations and adverse event reporting will be performed to determine the safety of the monthly injections. Risperidone oral tablets, 2 to 6 milligrams per day, for first 2 weeks; long-acting risperidone intramuscular injections, 50 mg in 2 milliliters of liquid, every 2 weeks for 1 month, then injections once a month for 48 weeks. Monthly injection dose may be increased to 75 mg in 2-mL if needed.

Inclusion Criteria:

• Diagnosis of schizophrenia or schizoaffective disorder
• stable with respect to disease symptoms and other medical conditions
• stable on antipsychotic therapy with oral risperidone 2 to 6 milligrams per day for 8 weeks before study
• if female, using birth control.

Exclusion Criteria:

• Hospitalized within 8 weeks of beginning the study
• at risk to self or others
• presence of liver or kidney damage
• use of oral antipsychotic drugs other than risperidone within the past 8 weeks, of injected antipsychotics within the past 6 months, of long-acting risperidone in an earlier study, of investigational drugs within the past 30 days, or of electroconvulsive therapy within the past 12 months
• pregnant or breast-feeding
• if female, not using birth control
• abusing drugs or alcohol.