OBJECTIVE: To determine the accuracy of the WatchBP Office ABI monitor for blood pressure measurement developed by the Microlife Company. METHODS: The device accuracy was tested in 85 subjects with a mean age of 54 ± 19 years. Their systolic and diastolic blood pressure (SBP/DBP) at entry was 141 ± 30/86 ± 19 mmHg, and upper arm circumference was 28 ± 5 cm. Initially, the data from 33 participants were examined according to the 2002 version of the European Society of Hypertension (ESH) protocol. An additional 52 subjects were then enrolled to fulfill the requirements of the British Hypertension Society (BHS) protocol. In all participants, sequential same arm measurements were performed by two trained observers. RESULTS: The device passed all three phases of the ESH protocol for SBP and DBP. For the BHS protocol the device was graded A for both SBP and DBP. The A/A grade was achieved in the low blood pressure category ( 160/100 mmHg). Mean blood pressure difference between device and observers in the first 33 subjects was -0.9 ± 5.5 mmHg for SBP and -2.2 ± 4.5 mmHg for DBP and in the 85 participants it was -1.2 ± 6.5 mmHg and -2.3 ± 5.1, respectively. CONCLUSION: These data show that the Microlife WatchBP Office ABI monitor satisfied the recommended ESH accuracy levels and achieved A/A grade of the BHS protocol across a wide range of BP.