Introduction: Congestive heart failure (CHF) is an important cause of hospital admissions and is associated with an increased risk for development of acute renal failure (ARF). The purpose of this study was to describe the incidence of ARF, to ascertain risk factors for its development, and to determine whether ARF impacts hospital outcomes. Methods: Review was conducted of 509 hospital medical records of patients hospitalized with a principal diagnosis of CHF during 2004. ARF was defined as an increase in serum creatinine of 0.5 mg/dl compared to the admission value. Multivariable analysis was used to identify independent predictors of ARF. Results: Most patients had reduced renal function at the time of admission with mean serum creatinine of 1.45 ± 0.72 and calculated creatinine clearance of 43.1 ml/min. ARF developed during the hospitalization in 21% of patients, with a peak increase in serum creatinine of 0.5–3.3 mg/dl. Most cases occurred on hospital days 4–6 (69.5% of cases). ARF was associated with increased risk for in-hospital mortality and increased length of hospital stay. Risk factors for ARF included diabetes, elevated admission serum creatinine and reduced serum sodium and echocardiographic demonstration of diastolic dysfunction. Neither diuretic nor ACEI/ARB treatment was associated with increased risk. Conclusion: ARF is a common complication among patients hospitalized for CHF, and is associated with increased risk for adverse outcomes. Certain clinical characteristics present at the time of admission help identify patients at increased risk.