Purpose An increase in age has been observed among patients admitted to the intensive care unit (ICU). Age is a well-known risk factor for ICU readmission and mortality. However, the epidemiology and clinical characteristics of ICU readmission of elderly patients (over 65 years) have not been studied. Methods This retrospective single-center cohort study was conducted in a total 122-bed ICU of a tertiary care hospital in Seoul, Korea. Total 85,413 patients were enrolled between January 1, 2007 and December 31, 2017. Results Totally, 29,503 patients were included in the study group, of which 2,711 (9.1%) had ICU readmissions. Length of stay (LOS) in ICU and in-hospital were longer, and 28-day and in-hospital mortality was higher in readmitted patients than in nonreadmitted patients (Table). Risk factors of ICU readmission included the sequential organ failure assessment score; presence of chronic heart disease, diabetes mellitus, chronic kidney disease, and transplantation; use of mechanical ventilation, vasopressors, renal replacement therapy. ICU readmission was an independent predictor of in-hospital mortality on multivariable analysis (odds ratio, 1.467; 95% confidence interval; 1.293-1.665; p < 0.001). Early readmission showed lower SOFA scores (p = 0.005), higher albumin (p < 0.001), lower creatinine (p = 0.002), and CRP (p = 0.001) than delayed readmission. Conclusions ICU readmissions occurred in 9.2% of elderly patients, which was associated with poor prognosis and higher mortality. Early readmission occurred in patients with better physiologic parameters than delayed readmission.