Understanding frailty is the key to identifying and predicting the health status of the older adults.  The Frailty Index , which utilizes an accumulation of various variables , is very useful in predicting a patient's health status as changes in the degree of frailty can be monitored.It remains unclear whether the frailty index has a meaningful predictive value for major outcomes such as mortality and intensive care unit (ICU) admission. Therefore, the author aimed to investigate the association between the frailty index and major outcomes based on nationwide cohort data from the Korean population.A total of 135,581 individuals who requested long-term care between 2009 and 2012 were enrolled in the study, and were followed-up until the end of 2020. A deficit-accumulation frailty index (range: 0–1; robust <0.15, pre-frail 0.15–0.24, mild-to-moderately frail 0.25–0.44, severely frail ≥0.45) was calculated using 41 variables at enrollment. Hazard ratios (HRs) and 95% confidence intervals (CI) were calculated using multivariate-adjusted Cox proportional hazards regression analysis.During the 6.30 years of follow-up, 92,336 cases of mortality were recorded. After adjustment, the HRs (95% CI) for mortality, compared to the robust group, were 1.27 (1.22−1.33) in the pre-frail group, 1.61 (1.55−1.67) in the mild-to-moderately frail group, and 2.32 (2.23−2.41) in the severely frail group (p for trend <0.001). Additionally, during the 5.49 years of follow-up for ICU admission with 40,070 cases, The HRs (95% CI) for ICU admission were 1.18 (1.11−1.26) in the pre-frail group, 1.39 (1.32−1.46) in the mild-to-moderately frail group, and 1.81 (1.72−1.90) in the severely frail group (p for trend <0.001).A significant increasing association depending on the stage of frailty according to FI was confirmed in our study (p for trend <0.001). Through this study, we confirmed that the HRs for mortality and ICU admission increased proportionate to the degree of frailty.In this large-scale nationwide cohort study of older adults, frailty was significantly associated with increased risks of mortality and ICU admission according to frailty stages measured by frailty index. It seems that the frailty index provides additional value in predicting severe major outcomes such as mortality and ICU admission.