Purpose: The pharmacology, pharmaceutics, clinical efficacy, adverse effects, cost, and dosage and administration of long-acting risperidone injection are reviewed. Summary: Risperidone is the first atypical antipsychotic available in a long-acting injectable formulation. After a single injection, significant plasma levels of the drug are achieved at week 3 and sustained through week 6, subsiding by weeks 7-8. Steady state is achieved after four injections. Peak levels are less than those seen with comparable doses of oral risperidone. A 12-week double-blind placebo-controlled study and a one-year open-label study demonstrated the efficacy, safety, and tolerability of long-acting risperidone injection in patients with schizophrenia and schizoaffective disorder. Those who were considered stable on their previous medication showed continued clinical improvement and an increase in health-related quality of life during a year of treatment with long-acting risperidone injection. In the 12-week study, risperidone was well tolerated, with adverse-effect rates similar to those seen with placebo. Weight gain with long-acting risperidone injection is similar to that found with oral treatment. Extrapyramidal symptom ratings have shown improvement from baseline following administration of this agent. Individuals with schizophrenia who previously received oral risperidone therapy have shown a reduction in prolactin levels after a switch to the long-acting formulation. Conclusion: With its unique tolerability and efficacy, long-acting risperidone injection has the potential to extend the benefits of assured medication delivery and improved long-term outcomes to more patients with schizophrenia.