Blood pressure (BP) independently predicts cardiovascular risk in affluent countries. [1][2][3][4][5] However, several studies have shown that awareness of hypertension and BP control is still suboptimal, 1 and thus effective strategies should be developed to improve BP control and adherence to therapy. One of the methods used to achieve these goals is represented by self-measurement of BP at home by automatic devices. Many studies have shown that BP self-measurement at home allows a better BP control in hypertension and has a greater prognostic value than office BP. 6,7 In addition, self BP measurement is more appealing to the patient than the customary procedure in the physician's surgery often causing long waits. Upper-arm automatic devices gave fresh impetus to home self-measurement because of their user friendliness, 8 the only conditions to be respected being adequate cuff dimensions and correct positioning of the cuff on the patient's arm. [9][10][11][12][13][14] For reasons of market penetration and following a general tendency to miniaturization, many wrist devices recently appeared on the market 15 having the advantage of being smaller and easier to fit than upper-arm monitors, 16 and today wrist devices are used by a large portion of people who measure their BP at home. 17 However, in spite of technical improvement, their reliability in real-life conditions is not unanimously accepted. [18][19][20] Accuracy of BP measurement at wrist largely depends on the difference in height between the wrist and the heart because of the confounding effect of the hydrostatic pressure caused by the limb blood column.21-23 Wrists kept at a higher level in comparison with the heart lead to a false lower, and wrists at a lower level lead to a false higher BP values. Very rarely do patients receive appropriate training from family doctors or other healthcare personnel. Instructions attached to commercial packages require a certain degree of personal discernment, i.e., a good cognitive pattern. Only a few models have a position sensor to verify that the wrist is placed properly at heart level, 24 but even for these devices, no study has evaluated their reliability in real-life conditions.The aim of the present study was to ascertain whether wrist home BP is performed reliably or an error is present in measurement, and to identify the determinants of this error if any.To verify the reliability of wrist BP self-measurement, we determined at a population level the upper-arm−wrist BP difference in the office under a doctor's supervision and then verified whether this difference was maintained during home self-measurement.Abstract-The reliability of blood pressure measurement with wrist devices, which has not previously been assessed under real-life circumstances in general population, is dependent on correct positioning of the wrist device at heart level. We determined whether an error was present when blood pressure was self-measured at the wrist in 721 unselected subjects from the general population. After training, blood p...