Objective: The Poincare plot is a two-dimensional state-space approach, where a timed signal is plotted against itself after a time delay, enabling determination of the dynamic nature of signals. Quantification of the Poincare plot is a candidate for estimating anesthesia-dependent changes in the electroencephalogram (EEG). Methods: In 20 patients, at four different states of anesthesia (0.5%, 1%, 2% and 3% sevoflurane), frontal EEG signals (10 s) were used to construct Poincare plots. The plot pattern was quantified by the standard deviation of the voltage dispersion along the line of identity (SD2), the standard deviation perpendicular to the line of identity (SD1) and their ratio (SD1/SD2), and compared using spectral EEG features. Results: A significant stepwise decrease in the SD1/SD2 ratio was observed with each stepwise increase in sevoflurane concentration (p < 0.001 for each). From 0.5% to 3% sevoflurane anesthesia, the ratio of relative beta power to delta power (beta/delta) was highly correlated with SD1/SD2 (R = 0.92). Conclusions: The Poincare plot of the frontal EEG can detect the significant changes in the depth of anesthesia induced by different sevoflurane concentrations. Significance: The Poincare plot is a useful technique for detecting the EEG changes induced by anesthesia. (C) 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.