Background: Accurate measurement of blood pressure (BP) is fundamental to monitoring and diagnosing many health conditions. Methods for measuring BP vary. Last year, HealthPartners Medical Group (HPMG) chose to implement an automatic oscillometric method (Omron device) across care delivery in place of the previously existing manual sphygmomanometermethod. Aims: To compare accuracy of BP measures in HPMG clinics at two time points: prior to implementation of Omron devices across care delivery and postimplementation. Methods: We collected paired BP readings from patients presenting to three HPMG clinics during each time point. For each patient, one BP was taken by a nurse at the clinic visit (manual BP pre-Omron, Omron BP post-Omron) and the other was taken by a researcher (Omron BP both time points). Mean BPs were calculated for each time point and mean of within-person differences was calculated to compare methods at each time point. Results: BPs were collected from 118 patients pre-Omron and 159 patients post- Omron. Average pre-Omron Clinic BP was 120/73 mmHg and average pre-Omron Research BP was 127/75 mmHg. Mean pre-Omron within-person difference was 6/2 mmHg. Average post-Omron Clinic BP was 125/75 mmHg, and average post-Omron Research BP was 120/71 mmHg. Mean post-Omron within-person difference was -5/-3 mmHg. Conclusions: We observed differences between methods at each time point. Direction of findings is unexpected, but plausible. Strong terminal digit preference in manual BPs suggests systematic measurement error in pre-Omron period, and supports evidence that the Omron device is accurate despite observed increase in mean clinic blood pressures.