ObjectivesIn 2019, the Korean National Patient Safety Incidents Inquiry was conducted in the Republic of Korea to identify the national-level incidence of adverse events. This study determined the incidence and detailed the characteristics of adverse events at 15 regional public hospitals in the Republic of Korea.MethodsMedical records data of 500 randomly selected patients (discharged in 2016) were extracted from each of the 15 studied hospitals and reviewed in 3 stages. First, for each hospital, 2 nurses independently reviewed the medical records, using 41 screening criteria. Second, 2 physicians independently reviewed the records of those patients with at least 1 screening criterion from the first stage for adverse events occurrence and their characteristics. Third, a 9-member committee conducted a final review and compiled the final adverse event report.ResultsAmong 7500 patients, 4159 (55.5%) had at least 1 screening criterion; 745 (9.9%) experienced 901 adverse events (incidence, 12.0%). By type of institution, adverse event incidence varied widely from 1.2% to 45.6%. In 1032 adverse events, the majority (33.5%) were “patient care–related.” By severity, the majority (638; 70.8%) were temporary, requiring intervention, whereas 38 (4.2%) resulted in death. The preventability score was high for “patient care–related” and “diagnosis-related” adverse events. Duration of hospitalization was extended for 463 (44.9%) adverse events, with “diagnosis-related” (30.8%) and “surgery/procedural-related” (30.1%) types extended by at least 21 days.ConclusionsA review of medical records aids in identifying adverse events in medical institutions with varying characteristics, thus helping prioritize interventions to reduce their incidence.