OBJECTIVES: The aim was to determine the prevalence of different degrees of kidney dysfunction and to examine their association with short-term and long-term outcomes in a large unselected contemporary heart failure population and some of its subgroups. We examined to what extent the different cardiac conditions and their severity contribute to the prognostic value of kidney dysfunction in heart failure. DESIGN: We studied 47 716 patients in the Swedish Heart Failure Registry. Patients were divided into five renal function strata based on estimated glomerular filtration rate (eGFR) using the Chronic Kidney Disease Epidemiology Collaboration equation. The adjusted association between kidney function and outcome was examined by Cox regression. RESULTS: 51% of the patients had eGFR <60 mL/min/1.73 m(2) and 11% had eGFR <30. There was increasing mortality with decreasing kidney function regardless of age, presence of diabetes, New York Heart Association NYHA class, duration of heart failure and haemoglobin levels. The risk HR (95% CI) persisted after adjusting for differences in baseline characteristics, severity of heart disease, and medical treatment: eGFR 60-89: 0.86 (0.79 to 0.95); eGFR 30-59: 1.13 (1.03 to 1.24); eGFR 15-29: 1.85 (1.67 to 2.07); and eGFR <15: 2.96 ([2.53 to -3.47)], compared with eGFR ≥90. CONCLUSIONS: Kidney dysfunction is common and strongly associated with short-term and long-term outcomes in patients with heart failure. This strong association was evident in all age groups, regardless of NYHA class, duration of heart failure, haemoglobin level, and presence/absence of diabetes mellitus. After adjusting for differences in baseline data, aetiology and severity of heart disease and treatment, the strong association remained.