Objective: To assess the accuracy of the professional oscillometric blood pressure (BP) monitor Microlife WatchBP Office in adults and children according to the American National Standards Institute/Association for the Advancement of Medical Instrumentation/International Organization for Standardization (ANSI/AAMI/ISO) 81060-2:2013 standard., Methods: Adults and children (aged 3-12 years) were recruited to fulfil the age, sex, BP and cuff distribution criteria of the ANSI/AAMI/ISO standard using the same-arm sequential BP measurement method. Three cuffs of the test device were used for arm circumferences of 14-22, 22-32 and 32-42 cm., Results: A total of 115 participants were recruited and 88 were included in the analysis (51 adults and 37 children). For criterion 1, the mean±SD of the differences between the test device and reference BP was -1.0±7.0/-4.7±5.4 mmHg (systolic/diastolic). For criterion 2, the SD of the averaged BP differences between the test device and reference per participant was 5.15/4.77 mmHg (systolic/diastolic)., Conclusion: The professional Microlife WatchBP Office BP monitor fulfilled the requirements of the ANSI/AAMI/ISO validation standard for adults and children and can be recommended for clinical use.