The aim of this study was to investigate impact of central blood pressure (BP) levels and sex on the difference between central and upper arm oscillometric BP values. Oscillometric arterial BP measurements of 675 patients were simultaneously compared with values measured from the ascending aorta. The patients were divided into 3 groups according to systolic BP levels. The upper arm oscillometric device overestimated systolic BP (SBP) at low and medium BP levels but it underestimated SBP at high BP level. As for the effect of sex on differences in central and oscillometric BP, SBP was overestimated to a lesser degree in women than in men at low BP levels, but it was more highly underestimated in women than in men at high BP levels. The difference between oscillometric upper arm BP and aortic BP was directly affected by the patient's central BP level. In addition, the difference between central and oscillometric BP was also affected by sex factor.