The purpose of this study is to examine the differences between elderly patients with unplanned readmissions and those without, and to identify influencing factors of unplanned readmissions among elderly patients. This study is a secondary data analysis based on a 2020-aged patient sample data from the Health Insurance Review & Assessment service. The study targeted patients aged 65 years or older who were hospitalized between January 1, 2020, and December 1, 2020. A total of 42,108 patient sample records were extracted. Data analysis included descriptive statistics, χ2 tests, t-tests, and logistic regression, performed using SAS Enterprise 4.3. Unplanned readmission varied significantly by gender (χ2 = 16.40, p < .001), age (χ2 = 209.74, p < .001), type of medical coverage (χ2 = 76.73, p < .001), primary diagnosis group (χ2 = 520.26, p < .001) and surgical status (χ2 = 641.61, p < .001). Among medical use-related factors, significant differences were observed in hospitalization route (χ2 = 121.10, p < .001), type of hospital (χ2 = 18.27, p < .001), number of beds in a hospital (χ2 = 78.30, p < .001), and length of hospitalization (t = −5.57, p < .001). Factors related to unplanned readmission included gender (B = 0.07, p < .001), age (B = 0.160, p < .001), surgical status (B = 0.400, p < .001), hospitalization route (B = 0.320, p < .001), and hospitalization period (B = 0.009, p < .001). This study confirmed that being male, older age, non-operative status, admission through the emergency room, and longer hospitalization were factors associated with unplanned readmissions. The use of nationwide data for the entire population aged 65 or older ensures the representativeness of these findings for elderly patients in South Korea. These findings can assist in identifying elderly patients at high risk of readmission, providing essential data for developing nursing interventions aimed at preventing unplanned readmissions among elderly patients.
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