This paper assesses the sensitivity and specificity of the electrocardiogram in detecting left ventricular hypertrophy in 75 hypertensive patients. Each patient underwent a 12 lead electrocardiogram and echocardiogram. Left ventricular mass index, using echocardiogram, was calculated according to the Penn convention and left ventricular hypertrophy was assessed by standard electrocardiographic criteria. The electrocardiogram was found to be very specific but insensitive in the detection of left ventricular hypertrophy as compared with the echocardiogram. Other non-voltage dependent markers appeared to have similar reliability. We conclude that the electrocardiogram may be unreliable in the detection of left ventricular hypertrophy in hypertensive patients. Accurate assessment of left ventricular hypertrophy, in these patients should be by echocardiography.