We examined the relationship of hypertension to left ventricular hypertrophy (LVH) and left ventricular diastolic function by ambulatory blood pressure monitoring device and echocardiography. We studied 36 untreated hypertensive non-diabetic patients (16 males and 20 females) whose casual systolic blood pressure (CSBP) and/or diastolic blood pressure (CDBP) were higher than 140 mmHg and 90 mmHg, respectively. All patients were less than 65 years of age without organic heart disease. Resting systolic and diastolic blood pressures (RSBP, RDBP) were measured after lying in a supine position for 30 min by the auscultatory method. Ambulatory blood pressure was measured every 30 or 60 min for 24 hours by Colin ABPM 630, and the mean 24-hour ambulatory systolic and diastolic blood pressures (ASBP, ADBP) and the systolic and diastolic hyperbaric indices (SHI, DHI) were obtained. The left ventricular mass index (LVMI) was obtained as an indicator of LVH by M-mode echocardiography. The ratio of peak velocity of mitral inflow caused by atrial contraction to that of rapid inflow (A/R) was obtained as an indicator of the LV diastolic function by Doppler echocardiography. The coefficients of correlation between BP and the LVMI, and the A/R were determined. There were significant positive correlations between the LVMI and ASBP (r = 0.51, p < 0.005), the SHI (r = 0.49, p < 0.005), CSBP (r = 0.47, p < 0.01) and RSBP (r = 0.41, p < 0.05), however, there were no significant correlations between the LVMI and ADBP, the DHI, CDBP, RDBP and age. There were significant positive correlations between the A/R and ADBP (r = 0.44, p < 0.01), age (r = 0.40, p < 0.02), CSBP (r = 0.38, p < 0.05) and RDBP (r = 0.38, p < 0.05), however, no significant correlations between the A/R and ASBP, the SHI, DHI, RSBP and CDBP. Only a weak correlation was observed in all subjects between the LVMI and A/R, which was slightly improved by use of > 90 mmHg CSBP readings (r = 0.32). It was concluded that LVH is related mainly to continuous systolic hypertension, and that LV diastolic dysfunction is related mainly to continuous diastolic hypertension. Therefore, it was suggested that LVH and LV diastolic dysfunction in hypertensive patients are caused by different mechanisms.