The aim of the study is to analyse the usefulness of electrocardiographic criteria of left ventricular hypertrophy in essential hypertension. Seventy four patients (27 males, 47 females), 49 +/- 11 years--old with mild--moderate systemic hypertension (blood pressure greater than or equal to 140/90 mmHg) have been prospectively studied. A 12-lead electrocardiogram and an echocardiogram (M and 2D mode) have been performed after the basic clinical study. A left ventricular mass index (Devereux's method) greater than 131 g/square meters (males) or greater than 110 g/square meters (females) has been considered as left ventricular hypertrophy. Sensitivity, specificity and accuracy of 11 current electrocardiographic criteria of left ventricular hypertrophy have been determined. Sensitivity of these criteria was very low (0-0.35), while specificity was high (0.71-1). Total QRS voltage showed the best accuracy (0.51), while V5 or V6 R wave amplitude greater than 26 mm showed the best sensitivity (0.35). Current electrocardiographic criteria of left ventricular hypertrophy are not very useful in the diagnosis of left ventricular hypertrophy in essential hypertension.