OBJECTIVE Up to one-third of all blood pressure devices sold are for measurement at the wrist. Wrist monitors are thought to be subject to errors associated with movement and incorrect posture. We used the British Hypertension Society protocol to determine the accuracy of the Omron Rx automated wrist blood pressure monitor in adults. We also investigated the errors associated with miscuffing and posture with measurements at the wrist compared to the upper arm. METHODS The study was conducted at a large teaching hospital in the UK. Participants 18 years and over were eligible for inclusion. Exclusion criteria were cardiac arrhythmias and inaudible Korotkoff sounds. Eighty-five participants were selected for the main validation study. Thirty-four subjects took part in the study investigating miscuffing issues and 15 subjects were included in the study investigating postural errors. RESULTS The Omron Rx achieved an overall grade B according to the British Hypertension Society Protocol. The mean differences (standard deviation) between the observers and the device were 0.3 (9.0) and 2.5 (8.8) mmHg for systolic and diastolic blood pressure respectively. In the medium and high-pressure ranges (> or =130/80 mmHg) the device achieved a grade C. When used at home the mean blood pressure reading over 60 measurements in 15 subjects was 123/75 mmHg when taken with the Omron Rx and 124/77 mmHg when taken with the automated upper arm device with no significant difference in the standard deviation of the readings. When compared with mercury sphygmomanometry using both a medium and large cuff, the wrist device readings were closest to the mercury measurements when the most appropriately sized cuff was used. CONCLUSIONS The Omron Rx wrist monitor is accurate according to the British Hypertension Society protocol, but narrowly fails the Association of the Advancement of Medical Instrumentation criteria. Measurements at the wrist are not associated with miscuffing errors. Use of the wrist device by patients in the home setting gives comparable readings to a standard upper arm device.