OBJECTIVES: The goal of this study was to determine the prognostic significance of estimated creatinine clearance (CrCl) in relation to 6-min walk distance in ambulatory patients with congestive heart failure (HF). BACKGROUND: Although measurement of renal function is integral to the management of chronic congestive HF, its prognostic implications are not well described and have not been formally evaluated relative to measures of functional capacity. METHODS: We analyzed outcomes of the 585 participants of the 6-min walk substudy of the Digitalis Investigation Group (DIG) trial. The CrCl was estimated using the Cockcroft-Gault equation. Predictors of all-cause mortality were identified using semiparametric Cox proportional hazards regression and completely parametric hazard analyses. RESULTS: Most subjects (85%) were New York Heart Association functional class II and III. Mean age was 65 (±12) years and mean ejection fraction (EF) 35% (±13%). There were 153 (26%) deaths during a median of 2.6 years of follow-up. Mortality by increasing quartiles of estimated CrCl was 37% (18 to 48 ml/min), 29% (47 to 64 ml/min), 18% (64 to 86 ml/min), and 21% (86 to 194 ml/min) with corresponding hazard ratios (HRs) relative to the top quartile of 2.1 (95% confidence interval [CI], 1.4 to 3.3), 1.6 (95% CI, 1.0 to 2.5), and 0.9 (95% CI, 0.5 to 1.5), respectively. In Cox regression analyses, independent predictors of mortality were estimated CrCl (adjusted HR [quartile 1:quartile 4] 1.5; 95% CI, 1.1 to 2.1), 6-min walk distance ≤262 m [adjusted HR, 1.63; 95% CI, 1.12 to 2.27]), EF, recent hospitalization for worsening HF, and need for diuretic treatment. Parametric (hazard) analysis confirmed consistent effects of estimated CrCl on mortality in several subgroups including that of patients with EF >45%. CONCLUSIONS: In ambulatory patients with congestive HF, estimated CrCl predicts all-cause mortality independently of established prognostic variables.