A 64-year-old woman was scheduled for the removal of hepatic cystadenoarcinoma. The preoperative examination did not reveal any neurological disorders. Anesthesia was induced with midazolam (5 mg) and remifentanil (0.1.ag x kg-1 x min-1) and the trachea was intubated following administration of rocuronium. Anesthesia was maintained with propofol (1.2-4.0 mg x kg-1 x hr-1), remifentanil (0.1-0.4microg kg 1 x min-1), and rocuronium (10 mg) as needed. The dose of propofol was controlled so that bispectral index (BIS) ranged between 40 and 60 during surgery. The duration of surgery was 10 hr 29 min. Administration of propofol and remifentanil was terminated at the end of surgery. After confirmation of T2 appearance by train-of-four stimuli, sugammadex (2 mg x kg 1) was intravenously administered. Although respiratory rate and tidal volume were 12-18 breaths x min-1 and 350-450 ml, respectively, she remained unconsciousness at about 40 of BIS. We could not find any factors associated with delayed emergence from anesthesia. Flumazenil (0.5 mg) was administered intravenously 90 min after termination of anesthesia. Two min later, she became fully awake and alert with increase in BIS (above 90). Laboratory examination showed that the plasma concentrations of propofol, midazolam, and its active metabolite alpha-hydroxymidazolam before administration of flumazenil were within the range considered to have no sedative effects. From experience of this case, administration of flumazenil may be beneficial for improvement in consciousness in cases with unexpectedly delayed emergence from anesthesia.