In patients with COPD, the maximal oxygen uptake (Vo2) measured at peak exercise and the 6-min walk distance (6MWD) have been associated with survival; however, no study has compared the strength of the association in the same patients. In this study, we compared the association between the 6MWD and peak Vo2 and mortality in 365 patients with COPD. Patients' cardiopulmonary cycle ergometry test results and 6MWD were determined at entry, and patients were followed up for a mean period of 67 months. There were 171 deaths. Compared with survivors, nonsurvivors were older (mean [+/- SD] age, 67.9 +/- 8 vs 65.9 +/- 8 years, respectively; p = 0.008), had worse mean FEV1 (36.5 +/- 12 vs 42.6 +/- 14 L, respectively; p = 0.02), had lower mean peak Vo2 (9.8 +/- 3 vs 11.8 +/- 3.6 mL/Kg/min, respectively; p < 0.0001), lower mean 6MWD (312 +/- 104 vs 377 +/- 95 m, respectively; p < 0.0001), and lower mean exercise minute ventilation (37.4 +/- 12 vs 42.3 +/- 13 L/min, respectively; p = 0.004). Univariate analysis showed that peak Vo2 and 6MWD as well as comorbidity, FEV1, and body mass index were associated with death. Logistic regression analysis with mortality as the dependent variable revealed that 6MWD (hazard ratio [HR], 0.996; 95% confidence interval [CI], 0.993 to 0.999; p < 0.01) had a stronger association than the peak Vo2 (HR, 0.971; 95% CI, 0.959 to 1.000; p = 0.050) with mortality. This study shows the 6MWD is as good predictor of mortality as the peak Vo2 in patients with COPD.