Renal impairment is often observed in acute heart failure (HF), which is an independent prognostic factor. It is important to identify high-risk patients, who need close follow-up and intensive care for renal protection. This study was conducted to identify the factors associated with the subsequent occurrence of HF-related renal dysfunction in patients, who were admitted to the hospitals due to acute HF symptoms. We evaluated 254 consecutive patients with acute HF. HF-related renal dysfunction was defined when highest serum creatinine level was greater than 1.2 mg/dl and the serum creatinine level increased by more than 50% compared with the baseline value during the admission. Forty patients with acute HF (16%) had subsequent renal dysfunction after admission. Elevated serum C-reactive protein (CRP) levels (> or = 5 mg/dl, odds ratio 2.51, p = 0.008 by univariate analysis, odds ratio 2.43, p = 0.019 by multivariate analysis) during the first week after admission and over-reduction of body weight (> or = 4.5 kg, odds ratio 2.68, p = 0.005 by univariate analysis, odds ratio 2.53, p = 0.010 by multivariate analysis) by acute HF treatment were significantly associated with this phenomenon. Patients with high CRP levels (> or = 5 mg/dl) during the first week after admission showed a significantly greater elevation of serum creatinine levels as compared to the levels before admission than those with low CRP levels (< 5 mg/dl). In conclsion, higher serum levels of CRP could predict the subsequent renal impairment in patients admitted with the worsening of HF symptoms.