BACKGROUND: The bispectral index (BIS), a parameter derived from the electro-encephalography (EEG), has been shown to correlate with the sedative state of anesthetic agents. This study was designed to evaluate the effect of BIS monitoring on anesthetic use and recovery characteristics in long duration sevoflurane anesthesia. METHODS: Forty adult patients who were scheduled for prolonged anesthesia (above 150 minutes) were randomly assigned to the control group (n = 20) or the BIS group (n = 20). In the control group, the anesthesiologists were blinded to the BIS values, and sevoflurane was administered according to standard clinical practice. In the BIS group, sevoflurane was titrated to maintain the BIS value between 45 60. Mean arterial pressure (MAP), heart rate (HR), end-tidal sevoflurane, BIS was monitored at intervals of 15 minutes. Time to response (TR), time to extubation (TE), time to reach 10 points of PAR score (TPAR10) and time to the discharge from postanesthetic care unit (TDis) were recorded from withdrawal of sevoflurane for recovery time. RESULTS: ET-Sevoflurane was significantly lower in the BIS group than the control group. BIS and 95% SEF values were higher in the BIS group compared with the control group. All values of recovery time (TR, TE, TPAR10, TDis) were significantly shorter in the BIS group than control group. In MAP and HR, there was no significant difference between the groups. CONCLUSIONS: BIS is considered a good index of proper use of sevoflurane. Decrease of total amount of sevoflurane, early emergence and early discharge from PACU are expected, so more safe and economic anesthesia may be possible in clinics.