ObjectiveArterial hypertension has a high prevalence in most countries. Blood pressure measurements are performed frequently by primary care physicians. Recommendations from different societies emphasise the importance of measuring blood pressure with well maintained and calibrated instruments only. Since appropriate quality control measures are lacking the following survey was conducted in the medical practices of Swiss primary care physicians.MethodsThis is a cross-sectional survey with Swiss primary care physicians. Nine hundred and seventy-five sphygmomanometers used in the daily practice of medicine were compared and calibrated against a certified calibrator. The magnitude of the measuring error before and after calibration was determined.ResultsThe proportion of the instruments that measured within the required tolerance of ± 3 mmHg over all measuring ranges was 81.4%. The average maintenance time was 5.6 years (± 3.8), and 97% (n = 353) of these instruments had not been maintained for two years (i.e. the recommended maintenance interval) or more. Two years after maintenance the number of devices with measurement errors of more than ± 3 mmHg increased significantly.ConclusionIn Swiss primary care practices, the majority of upper arm and wrist sphygmomanometers measured blood pressure within a tolerance of ± 3 mmHg despite low adherence to the recommended maintenance interval. Two years after maintenance the number of sphygmomanometers with measurement errors increased significantly.