BACKGROUND: In older adults admitted to intensive care units (ICUs), frailty influences prognosis. We examined the relationship between the frailty index (FI) based on deficit accumulation and early and late survival. METHODS: Older patients (≥65 years) admitted to a specialized geriatric ICU at the Liuhuaqiao Hospital, Guangzhou, China between July-December 2011 (n = 155; age 82.7±7.1 y; 87.1% men) were followed for 300 days. The FI was calculated as the proportion present of 52 health deficits. FI performance was compared with that of several prognostic scores. RESULTS: The 90-day death rate was 38.7% (n = 60; 27 died within 30 days). The FI score was correlated with the Glasgow Coma Scale, Karnofsky Scale, Palliative Performance Scale, Acute Physiology Score-APACHE II and APACHE IV (r (2) = 0.52 to 0.72, p < 0.001). Patients who died within 30 days had higher mean FI scores (0.41±0.11) than those who survived to 300 days (0.22±0.11; F = 38.91, p < 0.001). Each 1% increase in the FI from the previous level was associated with an 11% increase in the 30-day mortality risk (95% CI: 7%-15%) adjusting for age, sex, and the prognostic scores. The FI discriminated patients who died in 30 days from those who survived with moderately high accuracy (AUC = 0.89±0.03). No one with an FI score >0.46 survived past 90 days. CONCLUSION: ICU survival was strongly associated with the level of frailty at admission. An FI based on health deficit accumulation may help improve critical care outcome prediction in older adults.