Accurate blood pressure (BP) measurement is dependent on a trained observer using validated and properly maintained equipment. BP devices should be checked regularly to ensure that their calibration remains within the European Standard specification of +/-3 mm Hg. This study assessed the air leakage rates and calibration accuracy of BP devices in use at a large teaching hospital, using a calibrated electronic pressure gauge as reference. Air leakage rates were recorded over 1 min and static pressures were recorded at 250/200/150/100/50/0 mm Hg for computer download and analysis. A total of 127 devices were assessed (18 mercury, 62 aneroid and 47 automated). In total, 22 different models of devices were available, of which 11 were automated and only 4 had published evidence of a validation using a recognized protocol (British Hypertension Society, Association for the Advancement of Medical Instrumentation or International Protocol). Only 3% (n=4) of devices had an air leakage rate within 4 mm Hg per min and 25% (n=32) of devices failed to meet the European calibration standard of +/-3 mm Hg. Respective failure rates were 6% (1/18) for mercury, 31% (19/62) for aneroid and 26% (12/47) for automated devices. Inaccurate BP measurement of only 3 mm Hg can have detrimental effects in the patient. This study shows a quarter of devices currently in use at a large teaching hospital to have an unacceptable calibration error. Regular maintenance and calibration checks are vital in ensuring that BP is measured as accurately as possible.