PURPOSE: The current study was done to identify individual- and group-level factors associated with health care service utilization among Korean medical aid beneficiaries by applying multilevel modeling. METHODS: Secondary data analysis was performed using data on health care service reimbursement and medical aid case management progress from 15,948 beneficiaries, and data from 229 regions were included in the analysis. RESULTS: Results of multilevel analysis showed an estimated intraclass correlation coefficient (ICC) of 18.1%, indicating that the group level accounted for 18.1% of the total variance in health care service utilization, and that beneficiaries within the region are more likely to share common features with regard to health care service utilization. At the individual level, existence of disability and types of medical aid beneficiaries showed a significant association, while, at the group level, social deprivation index, and the number of beneficiaries and case managers within the region showed a significant association with health care service utilization. CONCLUSION: The significant influence of group level variables in health care service utilization found in this study indicate a need for group level approaches, such as policy change and/or promotion of community awareness.