To evaluate the surface (12 derivations) electrocardiogram in its possibility to predict left ventricular hypertrophy, the diastolic thickness of the posterior wall of the left ventricle was determined by M mode echocardiography in 12 normal persons and 47 hypertensive patients. In all cases the echocardiographic findings concerning diastolic thickness of the free wall of the left ventricle were studied as well as their relation ship to several electrocardiographic criteria mentioned in literature as indicative of left ventricle hypertrophy. The sensitivity, specificity and precision were calculated for each EKG criterion. The electrocardiographic criteria in general are little sensitive, highly specific and very variable in its accuracy. The most sensitive criteria found as indicative of left ventricle hypertrophy were the T positive wave in V1 higher than the T in V6 and the intrinsecoid deflection time inscription higher than 0.04 sec.