Background and Objectives: The applanation tonometry using Sphygmocor system has been proposed as a non-invasive method of estimating central aortic pressure. This system relies on mathematically derived generalized transfer function. We ought to compare simultaneous estimates of central aortic pressure using this system, to those measured directly during the diagnostic coronary angiography. Methods: Ascending aortic pressure and brachial artery pressure waves were recorded with the cardiac catheter in situ simultaneously in 30 patients undergoing coronary angiography. At the same time we estimated central aortic pressure by Sphygmocor system caliberated using the invasively measured brachial artery blood pressure. Result: There was close linear correlation between the invasively measured aortic pressure and the estimated aortic pressure by Sphygmocor system. But Sphygmocor system significantly underestimated the invasively measured aortic systolic blood pressure( mean 짹SD: 7.80 짹7.32 mmHg, P < 0.0001). The estimated diastolic blood pressure was not significantly different from the invasively measured central aortic diasolic blood pressure. Conclusion: Although estimated central aortic pressures derived from the Sphygmocor system correlated well with those obtained invasively, the system significantly underestimated the invasively measured aortic systolic pressure. Therefore, it may be that the transfer function should be redesigned to be used clinically.