Objective: Frequent emergency department (ED) visitors may be medically vulnerable subjects who could benefit from interventions that both reform care and lower costs. In this study, we identified characteristics of “frequent ED users” among Korean patients with type 2 diabetes mellitus (DM). Methods: We utilized the HIRA-NPS (Health Insurance Review and Assessment service national patient sample), which is a nationally representative sample extracted by stratified sampling. Subjects (n = 109,412) who had type 2 DM as a primary or secondary diagnosis at one of their visits were considered in the analysis. Individuals were classified into three groups according to the number of ED visits: frequent (≥ 4 visits), occasional (< 4 visits) and non-users of the ED. The characteristics of the patients with DM that distinguished frequent users from the other groups were investigated. Results: Frequent ED users with type 2 DM were mainly male (P < 0.001) and had longer treatment duration (P < 0.001), more frequent co-morbidities (cardiovascular disease and chronic kidney disease) and a primary diagnosis with surgery (P = 0.0028). They showed higher mortality (P = 0.0085), longer hospitalization duration (P < 0.001), higher costs per visit (p < 0.001), and more often presented medical protection (P < 0.001). Regarding the usual taken drugs, patients in this group, were treated more frequently with Sulfonylurea, Insulin, Meglitinide, alpha-glucosidase inhibitor (AGI) (P < 0.05). Conclusion: Frequent users of the ED with type 2 DM have serious health conditions (such as chronic kidney disease), poor socioeconomic situation and tend to take more frequently some medicines (like Sulfonylurea, Insulin etc.) associated with Hypoglycemia. Therefore, it should be given more attention on the therapy and on patients with renal and cardiovascular diseases in order to decrease the dependency of these patients on the ED.