Large artery intima-media thickness (IMT) is considered an integrated marker for the total individual burden of arteriosclerosis, and a graded index for cardiovascular risk. However, several different aggregate indexes of IMT on B-mode ultrasound have been used by various investigators, and the optimal number of IMT readings is currently unsettled. In 128 newly diagnosed, never treated, uncomplicated hypertensive subjects aged <55 years (43 +/- 9 years, blood pressure [BP] 152/99 mm Hg), we measured left ventricular mass (M-mode echocardiography, average of five or more measurements) and IMT of common carotid and common femoral arteries. For each segment, 12 IMT measurements were performed, and the average of 1 and 3 readings (right far wall), 6 readings (right side), and 12 readings (right and left side, far and near wall, 3 sampling points) was analyzed. The relation of IMT with left ventricular mass increased progressively with increasing number of readings, from 0.35 (1 reading) to 0.51 (12 readings) for common carotid artery, and from 0.31 to 0.56 for common femoral artery (both P <.001). For each 0.2-mm increase in common femoral IMT, the age-adjusted relative risk of having left ventricular hypertrophy was 1.31 for 1 reading, and increased up to 3.59 for the average of 12 readings. In summary, the association of IMT with left ventricular mass depends strongly on the number of IMT readings. The average of several readings in each segment, including right and left side and far and near wall, carries the closest association to left ventricular mass, and should be preferred for clinical purposes in hypertensive subjects.