BACKGROUND The plasma brain natriuretic peptide (BNP) level in elderly patients is elevated, but the mechanism of this increase is not clear. OBJECTIVE To examine the relationship between left ventricular geometry and BNP levels in elderly subjects. METHODS We investigated the effects of left ventricular (LV) geometry on plasma BNP levels by measuring these levels in elderly patients with or without LV hypertrophy. Patients were classified into 4 groups based on echocardiographic data: normal geometry; concentric remodeling; eccentric hypertrophy (EH), and concentric hypertrophy (CH). The samples were analyzed for BNP and endothelin-1 (ET-1). RESULTS Among the 4 groups, there were no differences in plasma ET-1 levels, ejection fraction, percent fractional shortening, or indices of diastolic function. Plasma BNP levels in EH and CH were higher than those in the normal geometry and concentric remodeling groups. There was a good correlation between plasma BNP levels and the relative wall thickness in EH, and between plasma BNP levels and the posterior wall thickness in CH (r = -0.474, r = 0.396, respectively, both p < 0.05). There were also good correlations between plasma BNP levels and LV mass index (LVMI). A stepwise multiple regression analysis showed that age and LVMI were significant independent contributors to plasma BNP levels. CONCLUSIONS These results suggest that aging, increased wall stress and the extent of cardiac hypertrophy contribute to elevated BNP levels in the elderly.