Purpose: We sought to assess mortality trends in chest-abdominal trauma patients, before and after the implementation of the Project Supporting Establishment of Trauma Centers (PSETC) in the Republic of Korea. Methods: Data from the National Health Insurance Service claims database between 2009 to 2017 were analyzed. Patients with chest-abdominal trauma were defined as those with relevant main diagnosis codes and claims for emergency medical management fees. Mortality and cumulative data were analyzed for each year to compare mortality before and after the establishment of regional trauma centers across Korea (2014). Results: In total, 29,127 patients were included in the analysis. While the annual incidence of trauma-related chest-abdominal injuries increased, mortalities decreased. In particular, the trauma incidence rate among patients over 50 years increased during the study period. Mortalities at trauma centers did not change year by year after the PSETC. Before and after 2014, when trauma centers operated under the PSETC, mortalities decreased [trauma cases before the PSETC; n = 14,321 (mortality 5.61), after the PSETC; n = 14,806 (mortality 4.96)]. Conclusion The number of patients treated for chest-abdominal injuries increased from 2009 to 2017 in Korea, whereas mortalities decreased over the same period.