OBJECTIVES The objective of this study was to compare the health care utilization and associated cost in a group of schizophrenia and schizoaffective patients pre and post risperidone long-acting injection (RLA) treatment. METHODS This was a retrospective cost analysis study. Data was gathered solely from hospital records, which were reviewed for data pertaining to utilization of health care resources. The study was performed from a public health care institute's perspective. Patients studied were from three public hospitals in Hong Kong. They were started on antipsychotic treatment but later on switched to RLA therapy due to adverse effects, poor response or whatever reasons and remained on risperidone for a minimum of 12 months. The initial RLA administration date served as the index date. Study periods included 12-month pre and 24-month post the index date and patients served as their own control. Cost data collected included medications, laboratory procedures, other more sophisticated investigational procedures (e.g. CT, MRI), regular and extra outpatient clinic visits, emergency room utilization, hospitalization, and other health services such as special counseling sessions. RESULTS A total of 180 patients who received RLA treatment were identified from 2 public general and 1 psychiatric hospitals in Hong Kong over the period of 2003-2006. The overall annual cost of treatment before and after RLA injection was HKD80.5 million (USD10.3 million; 1USD=7.8HKD) and HKD26 million (USD3.34 million) respectively. The annual average cost per patient before and after RLA treatment was HKD447,300 (USD57,300) and HKD144,600 (USD18,500) respectively. CONCLUSIONS From the present group of patients assessed two years after initiation of RLA treatment, it appears that the treatment can potentially lead to substantial cost savings. The major cost driver appears to be hospitalization due to either poor control or adverse effects of medications.