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In the elderly, monitoring depth of anaesthesia seems to be of particular importance. We evaluated the bispectral index (BIS) for monitoring depth of anaesthesia during clinically guided balanced xenon or sevoflurane anaesthesia in aged patients.In this randomized controlled clinical trial, 40 patients (65–75 years) undergoing elective noncardiac surgery were randomly assigned to balanced anaesthesia with either 53.2 ± 0.8% xenon (n = 19) or 1.6 ± 0.1% sevoflurane (n = 20) in minimum 30% oxygen and remifentanil titrated to clinical needs. Depth of anaesthesia was guided by end-tidal gas concentrations and clinical signs. The attending anaesthesiologist was blinded to the BIS values, which were recorded at 1 min rates during induction, at 5 min rates during maintenance and at 20 s rates during emergence. Emergence from anaesthesia was assessed by the times to open eyes, react on demand, extubation and orientation.During induction and maintenance of anaesthesia, BIS values in the xenon group were comparable to sevoflurane and at the lower limit of the recommended range for deep anaesthesia. Emergence to full orientation was significantly faster from xenon than from sevoflurane. BIS values were significantly lower during emergence from xenon anaesthesia.During xenon and sevoflurane anaesthesia in the elderly, BIS-values show sufficient concordance with clinical signs of anaesthetic depth. Since during clinically guided anaesthesia values were at the lower recommended limit, additional BIS monitoring may help reduce anaesthetic consumption and costs.