BACKGROUND: Epidemiological findings, based largely on middle-aged populations, support an inverse and independent association between exercise capacity and mortality risk. The information available in older individuals is limited.METHODS AND RESULTS: Between 1986 and 2008, we assessed the association between exercise capacity and all-cause mortality in 5314 male veterans aged 65 to 92 years (mean+/-SD, 71.4+/-5.0 years) who completed an exercise test at the Veterans Affairs Medical Centers in Washington, DC, and Palo Alto, Calif. We established fitness categories based on peak metabolic equivalents (METs) achieved. During a median 8.1 years of follow-up (range, 0.1 to 25.3), there were 2137 deaths. Baseline exercise capacity was 6.3+/-2.4 METs among survivors and 5.3+/-2.0 METs in those who died (P<0.001) and emerged as a strong predictor of mortality. For each 1-MET increase in exercise capacity, the adjusted hazard for death was 12% lower (hazard ratio=0.88; confidence interval, 0.86 to 0.90). Compared with the least fit individuals (< or =4 METs), the mortality risk was 38% lower for those who achieved 5.1 to 6.0 METs (hazard ratio=0.62; confidence interval, 0.54 to 0.71) and progressively declined to 61% (hazard ratio=0.39; confidence interval, 0.32 to 0.49) for those who achieved >9 METs, regardless of age. Unfit individuals who improved their fitness status with serial testing had a 35% lower mortality risk (hazard ratio=0.65; confidence interval, 0.46 to 0.93) compared with those who remained unfit.CONCLUSIONS: Exercise capacity is an independent predictor of all-cause mortality in older men. The relationship is inverse and graded, with most survival benefits achieved in those with an exercise capacity >5 METs. Survival improved significantly when unfit individuals became fit.