Left ventricular (LV) hypertrophy and LV diastolic dysfunction are common cardiac changes in hypertensive patients, and these changes are modified by various factors other than blood pressure. The present study was conducted to investigate the influence of mild abnormalities in glucose metabolism on LV structure and function in essential hypertension. In 193 nondiabetic patients with treated essential hypertension, two-dimensional and Doppler echocardiographic examinations were performed, and relative wall thickness (RWT), LV mass index (LVMI), fractional shortening, and the ratio of the peak velocity of atrial filling to early diastolic filling (A⁄E) were calculated. Fasting plasma glucose (FPG) and HbA_1c levels were positively correlated with the A⁄E ratio and the deceleration time of the E wave. However, these plasma levels had no correlation with RWT, LVMI, or fractional shortening. Peak A wave velocity and the A⁄E ratio were significantly higher in patients who had FPG of ≥100 mg⁄dl (and <126 mg⁄dl) than those who had FPG of <100 mg⁄dl, although age, blood pressure, RWT, LVMI, and fractional shortening did not differ between the two groups. In a multiple regression analysis of all subjects, only FPG and age were independent determinants of the A/E ratio. These observations suggest that FPG is a sensitive predictor for LV diastolic dysfunction in nondiabetic patients with treated hypertension. Since a slight increase in plasma glucose levels is associated with abnormalities in diastolic function independent of LV hypertrophy, an early stage of impaired glucose metabolism in hypertensive patients may specifically deteriorate cardiac diastolic function. (Hypertens Res 2002; 25: 403-409)