Background:This study used the National Emergency Department Information System (NEDIS) data to analyze the flow of emergency and critical emergency patients and to identify the patts of emergency medical service usage in Korea.Methods:The relevance index (RI) and commitment index (CI) were calculated from the 2016 NEDIS data.In this study,the number of clusters was determined using NbClust,and cluster analysis was used to analyze the usage patts of emergency and critical emergency patients.Results:The RI and CI were calculated using 8,389,766 cases of 214 districts.The results of the RI and CI suggested that there were 3 types of clusters among the emergency patients.In Cluster 1,54 districts (25.2％) had low RI and high CI,and it was of outflow type.Cluster 2 was categorized as the influx-type in 58 districts (27.1％) irrespective of RI and low CI.Cluster 3 was categorized as the self-sufficient type found in 102 districts (47.7％),with high RI and high CI.The cluster analysis of the critical emergency patients was divided into 2 types.Cluster 1 was categorized as outflow type with high CI found in 129 districts (60.3 ％),while Cluster 2 was categorized as inflow type with low CI found in 85 districts (39.7％).Conclusions:This study elucidates the regional status of usage patts of emergency and critical emergency patients in Korea.This study might serve as a basis for the establishment and selection of emergency medical service areas and vulnerable emergency medical service areas.