Background The Cornell product (CP) improved identification of left ventricular hypertrophy (LVH) in the LIFE study, although its clinical significance is still unknown in Japanese hypertensive (HT) patients. Methods and Results A standard 12-lead ECG was recorded in 265 HT and 363 normotensive cases (N). All ECGs were digitized, and a simple product was calculated by multiplying the Cornell voltage (CV) by the QRS duration. In 147 of the 265 HT cases, the standard 12-lead ECG and transthoracic Doppler echocardiography were examined in the same period. The mean value of CP increased in the following order: 1,426±673 mm · ms in N, 1,989±900 mm · ms in HT with treatment, 2,137±976 mm · ms in HT without treatment. The correlation with left ventricular mass index (LVMI) measured by echocardiography was improved by CP with the simple CV. With use of a partition of 2,440 mm · ms in CP, LVMI and relative wall thickness were significantly higher in HT with ≥2,440 mm · ms of CP compared with <2,440 mm · ms. Early diastolic wave in tissue Doppler imaging was significantly lower in HT with ≥2,440 mm · ms of CP compared with <2,440 mm · ms. Conclusion The Cornell product is a useful ECG marker, reflecting not only left ventricular (LV) mass but also LV geometry and diastolic function in Japanese HT patients. (Circ J 2007; 71: 731 - 735)