To determine the accuracy of the large–extra large-sized (L–XL) cuff (32–52 cm) coupled to a Microlife WatchBP Office ABI blood pressure measuring device tested according to the requirements of the International Protocol of the European Society of Hypertension. The L–XL cuff tested in this study is designed to provide accurate blood pressure measurements in patients with large arms (arm circumference≥32 cm) over a wide range of arm circumferences using a single 145±1×320±1 mm bladder. The evaluation was made in 33 patients with a mean±standard deviation age of 53±17 years (range: 30–96 years). Their systolic blood pressure (SBP) was 142±21 mmHg (range: 110–180 mmHg), diastolic blood pressure (DBP) was 87±14 mmHg (range: 62–106 mmHg) and arm circumference was 36±5 cm (range: 32–50 cm). Blood pressure measurements were made in the sitting position. The L–XL cuff coupled to the WatchBP Office ABI passed all three phases of the European Society of Hypertension protocol for SBP and DBP. Mean blood pressure differences between device and observer were −1.3±5.1 mmHg for SBP and −1.8±5.8 mmHg for DBP. Similar device–observer differences were observed in patients divided into two subgroups according to whether their arm circumference was above or below the median in the group. These results indicate that the L–XL cuff coupled to the WatchBP Office ABI monitor provides accurate blood pressure readings in patients with large arms over a wide range of arm circumferences.