Background: Recent studies have shown that obesity is an independent predictor of lower N-terminal pro-BNP (NT-proBNP) levels and raised concerns about the validity of this biomarker in obese subjects. BNP has been shown to be increased in patients with DM, even in the absence of structural heart disease, and obesity frequently coexists with diabetes, so it is important to consider the joint influences on natriuretic peptide levels. So we evaluated the influence of diabetes on the correlation BNP and BMI. Methods: Simultaneous NT-proBNP and echocardiographic examinations were performed in 933 patients with dyspnea undergoing cardiac catheterization between Feb. 2006-Nov.2007 in Maryknoll cardiac center who had creatinine of <2.0, no evidence of systolic heart failure. Patients were divided into body mass index (BMI) >25kg/m2 (obese), 23 to 25 (overweight), and <23 kg/m2 (non obese). NT-proBNP levels, mitral early diastolic/tissue Doppler annular velocity (E/Ea), left ventricular (LV) geometry pattern using relative wall thickness and LV mass index and myocardial performance index(Tei index) were compared with groups. Results:In 733 non-diabetic patients, mean plasma NT-proBNP levels were significantly lower in obese (n=287, 289.62짹 164.9 pg/ml) and overweight patients(n=216, 601.69짹159.6 pg/ml) compared with nonobese patients(n=230, 856.39짹237.3 pg/ml)(p<0001, respectively). However, in 200 diabetic patients, there was no correlation between BMI and NT proBNP( 963.19짹223.7 pg/ml, 1450.15짹457.3 pg/ml, 658.05짹147.1pg/ml)(r=-0.91,p=0.19).NT-proBNP did not correlate with mitral E/Ea in obese diabetic patients (r= 0.14, p= 0.56), whereas NT-proBNP significantly correlated with this variable in the non obese (r=0.24) and non diabetic (r=0.32) groups. However, LV mass index was significantly correlated with NT-pro-BNP all BMI groups(r=0.61,p<0.001), and patients with concentric hypertrophy showed the highest BNP levels. Conclusion: The present study demonstrates that NT-proBNP is not suppressed in obese patients with diabetes and the correlation between plasma BNP and LV mass index was more robust than any other echocardiographic or hemodynamic parameter as well as any patient���s characteristics.