The Philips Intellivue MP50 monitor provides a method for non-invasive, near-continuous blood pressure (BP) monitoring and is designed to be an alternative to direct intra-arterial BP (IABP) measurement. However, no studies have specifically compared non-invasive and invasive BP measurements using the monitor. The present retrospective study observed 515 patients undergoing surgery with general anesthesia, whose invasive (intra-radial, femoral or dorsalis pedis artery) and non-invasive (oscillometric) BP (NIBP) were monitored simultaneously using the monitor. These data were analyzed using correlations, regressions and Bland-Altman plots. The patients were placed in a supine position during surgery. The correlation data for invasive BP and NIBP measurements were: for intra-radial measurements, r(2)=0.51 (bias and precision, 11.04 +/- 15.22 and 14.76 +/- 11.64 mmHg, respectively) for systolic BP (SBP) and r(2)=0.27 (6.17 +/- 11.95 and 9.77 +/- 9.25 mmHg, respectively) for diastolic BP (DBP); for intra-femoral measurements: r(2)=0.57. (14.79 +/- 14.55 and 17.15 +/- 11.68 mmHg, respectively) for SBP and r(2)=0.45 (4.12 +/- 9.70 and 7.49 +/- 7.40 mmHg, respectively) for DBP; and for intra-dorsalis pedis measurements: r(2)=0.33 (13.00 +/- 16.81 and 17.34 +/- 12.28 mmHg, respectively) for SBP and r(2)=0.30 (0.17 +/- 11.27 and 8.44 +/- 7.46 mmHg, respectively) for DBP. According to this data, the NIBP measured by the Philips Intellivue MP50 monitor showed low positive correlations and poor agreement with the IABP, as calculated by Bland-Altman analysis. Therefore, the use of oscillometric BP measured by the monitor in surgery patients under general anesthesia is not generally recommended.