BACKGROUND: The US Preventive Services Task Force recommends out-of-office blood pressure (BPs) before making a new diagnosis of hypertension, using 24-h ambulatory (ABPM) or home BP monitoring (HBPM), however this is not common in routine clinical practice. Blood Pressure Checks and Diagnosing Hypertension (BP-CHECK) is a randomized controlled diagnostic study assessing the comparability and acceptability of clinic, home, and kiosk-based BP monitoring to ABPM for diagnosing hypertension. Stakeholders including patients, providers, policy makers, and researchers informed the study design and protocols. METHODS: Adults aged 18-85 without diagnosed hypertension and on no hypertension medication with elevated BPs in clinic and at the baseline research visit are randomized to one of 3 regimens for diagnosing hypertension: (1) clinic BPs, (2) home BPs, or (3) kiosk BPs; all participants subsequently complete ABPM. The primary outcomes are the comparability (with daytime ABPM mean systolic and diastolic BP as the reference standard) and acceptability (e.g., adherence to, patient-reported outcomes) of each method compared to ABPM. Longer-term outcomes are assessed at 6-months including: patient-reported outcomes, primary care providers' diagnosis of hypertension; and BP control. We report challenges experienced and our response to these. RESULTS: Enrollment began in May of 2017 with a target of randomizing 510 participants. BP thresholds for diagnosing hypertension in the US changed after the trial started. We discuss the stakeholder process used to assess and respond to these changes. CONCLUSION AND PUBLIC HEALTH IMPACT: BP-CHECK will inform which hypertension diagnostic methods are most accurate, acceptable, and feasible to implement in primary care.