Objective: Long-acting injectable (LAI) antipsychotics, such as paliperidone palmitate (PP), are known to improve treatment adherence in patients with schizophrenia, which can lead to reductions in relapse and hospitalization rates. However, relatively few studies have demonstrated the economic impact of LAIs, especially in Asian populations. Methods: We conducted a claim-based mirror-image study to explore changes in healthcare utilization and associated costs, among 1,272 South Korean patients with schizophrenia (ICD-10-CM code F20), between the 1-year periods before and after the initiation of PP treatment. Results: Patients accessed outpatient services more frequently after versus before starting PP treatment, with the number of prescription days increasing by 133.45 (p < 0.0001) and the associated costs increasing by USD 1,497.15 (p < 0.0001). The number of admission days was reduced by 11.33 after starting PP treatment (p < 0.0001) and the associated costs were reduced by USD 1,220.75 (p < 0.0001). However, admission cost savings were different according to patients' oral drug compliance. The daily dosages for benztropine, procyclidine, and propranolol decreased, showing that there were fewer side-effects after PP-treatment (p < 0.0001). Conclusion: Although the high acquisition cost of PP has been regarded as an obstacle to its clinical use, our results imply that the high prescription costs for PP may be counterbalanced by the reduced admission costs associated with its use. Economic outcomes for patients treated with LAIs should be investigated further to help healthcare decision-makers and providers to determine the value of LAIs relative to other treatment medications.