Objective: As laboratory diagnostic tool to define heart failure (HF), plasma BNP level is widely used. But BNP level has been known to also increase in patients with renal insufficiency (RI). The aim of this study was to evaluate the diagnostic value of BNP level for heart failure in patients with RI. Methods: Between Aug 2002 and May 2004, 499 patients that were diagnosed HF or renal insufficiency were included. Patients��� clinical profile, echocardiographic parameters, plasma BNP (Triage, Biosite) level and other laboratory parameters were analyzed on admission. We classified patients into 3 groups (patients with only HF, with only RI, and with concomitant HF and RI). Heart failure was defined via using an echocardiography and Framingham clinical criteria. We calculated creatinine clearance (Ccr) with Cockcroft-Gault equation. RI was defined as in patients with lower Ccr (less than 50 ml/min). As severity of RI, patients were divided into 3 groups (mild; 35���Ccr<50, moderate; 20���Ccr<35, severe; Ccr<20ml/min). Results: 1. Mean age was 67짹13 and male was 47.9% (n=239). 2. There were statistically significant difference in plasma BNP level between 3 groups (p=0.00); group with only HF (n=137, 724.7짹757.1pg/ml), with only RI (n=167, 1330.0짹1536.4pg/ml), with concomitant HF and RI (n=195, 1909.5짹1555.3pg/ml). In patients with RI, there was statistically significant negative correlation between BNP level and Ccr (n=332, r=-0.366, p=0.00). As renal function deteriorate, BNP level increased significantly (mild; 1219.7짹1153.2, moderate; 1361.6짹1306.8, severe; 2547.7짹1895.4pg/ml, p=0.01). 3. As a ROC curve, diagnostic accuracy of BNP level in diagnosing HF in patients with RI was 64.6% with sensitivity,60.5% and specificity,65.7% (p=0.01). This was the significantly lower value than that of previous study about BNP level as diagnostic tool of HF (accuracy 98.0%). Conclusions: As renal dysfunction, BNP level was significantly elevated. Therefore, as it was diagnosed HF with renal insufficiency, we should consider higher cut-off point of BNP to diagnose Heart failure and relatively lower diagnostic accuracy of BNP.