Risperidone is a recently approved atypical antipsychotic that offers the advantages over existing typical antipsychotics of improved efficacy against negative symptoms and a decreased incidence of extrapyramidal side effects. However, risperidone is much more expensive than other antipsychotics. A drug use evaluation (DUE) was undertaken to assess the prescribing practices of risperidone in a large public adult psychiatric outpatient clinic. After a through literature review, criteria describing the appropriate prescribing of risperidone were approved after consultation with the medical staff. Criteria were developed to delineate appropriate patient selection, laboratory and clinical monitoring parameters, documentation, and outcome measures. After a chart review was conducted to evaluate existing prescribing practices, the criteria and results were presented to the medical staff and the appropriateness of the criteria were discussed. After 1 month, a second chart review was conducted to evaluate changes in prescribing practices in response to these criteria. Risperidone was prescribed to 44 patients in the outpatient clinic. Sixteen of these patients were resistant to treatment with traditional antipsychotics, 19 had developed intolerable extrapyramidal side effects during treatment with traditional antipsychotics, 10 had developed tardive dyskinesia, and 11 were noncompliant with other treatment regimens (some patients fell into more than one category). In 35 patients able to be evaluated for side effects, the most common were termed "activating side effects" and included restlessness, anxiety, insomnia, and unspecified activation. These side effects occurred in 9 patients. Another 5 patients developed extrapyramidal side effects and 3 patients developed a tremor. The initial chart review showed deficiencies in several areas, including laboratory and clinical monitoring and documentation. After presentation of these results to the staff, a second review was conducted; the results demonstrated improvements in many of the areas that were originally deficient. In conclusion, it was shown that the criteria developed had an overall positive impact on the appropriate prescribing of risperidone.