Frailty is a key determinant of clinical outcomes. We sought to describe frailty among U.S. Veterans and its association with mortality. Nationwide retrospective cohort study of regular Veterans Affairs (VA) users, aged at least 65 years in 2002-2012, followed through 2014, using national VA administrative and Medicare and Medicaid data. A frailty index (FI) for VA (VA-FI) was calculated using the cumulative deficit method. Thirty-one age-related deficits in health from diagnostic and procedure codes were included and were updated biennially. Survival analysis assessed associations between VA-FI and mortality. A VA-FI was calculated for 2,837,152 Veterans over 10 years. In 2002, 35.5% were non-frail (FI = 0-0.10), 32.6% were pre-frail (FI = 0.11-0.20), 18.9% were mildly frail (FI = 0.21-0.30), 8.7% were moderately frail (FI = 0.31-0.40), and 4.3% were severely frail (FI > 0.40). From 2002 to 2012, the prevalence of moderate frailty increased to 12.7%and severe frailty to 14.1%. Frailty was strongly associated with survival and was independent of age, sex, race, and smoking; the VA-FI better predicted mortality than age alone. Although prevalence of frailty rose over time, compared to non-frail Veterans, 2 years' hazard ratios (95% confidence intervals) for mortality declined from a peak in 2004 of 2.01 (1.97-2.04), 3.49 (3.44-3.55), 5.88 (5.79-5.97), and 10.39 (10.23-10.56) for pre-frail, mildly, moderately, and severely frail, respectively, to 1.51 (1.49-1.53), 2.36 (2.33-2.39), 3.68 (3.63-3.73), 6.62 (6.53-6.71) in 2012. At every frailty level, risk of mortality was lower for women versus men and higher for blacks versus whites. Frailty affects at least 3 of every 10 U.S. Veterans aged 65 years and older, and is strongly associated with mortality. The VA-FI could be used to more accurately estimate life expectancy and individualize care for Veterans.