OBJECTIVES: To investigate the predictive capacity of an age-related deficit accumulation index (the so-called Frailty Index [FI] proposed by Rockwood) for hospital admission (HA) and number of days spent in hospital (DSH) among nursing home residents. DESIGN, SETTING AND PARTICIPANTS: Data are from a longitudinal cohort study, the Incidence of pNeumonia and related ConseqUences in nursing home Residents (INCUR), of 768 elder people (75.4% women) living in 13 nursing homes in France. MEASUREMENTS: The FI was computed taking into account 30 possible deficits at the baseline visit. Hospital admissions were defined as all urgent and involuntary admissions including unplanned readmissions. The length of stay was the total number of days spent by the resident in the hospital. Cox proportional hazard models in the presence of competing risks (death) were performed to study the relationship between the FI and HA over a 12-month follow-up. A Zero-inflated negative binomial regression was performed to study the association between the FI and DSH. RESULTS: Mean age of participants was 86.7 (standard deviation [SD] 6.9) years, with a mean FI of 0.37 (SD 0.11). At the end of the follow-up, 238 (30.9%) HA events were recorded. Positive associations of the FI with DSH and HA were reported (per 0.01 FI increment: age- and gender-adjusted hazard ratio 1.15, 95% confidence interval 1.020-1.297, p=0.02 and OR 1.209 (1.075 - 1.359, p<0.001, respectively). CONCLUSIONS AND IMPLICATIONS: The FI is a strong predictor of negative health-related outcomes as HA and DSH events, even with very old and complex nursing home residents.