Background: Bispectral index is an accepted monitoring to assess the depth of anaesthesia and helps the anaesthesiologist to prevent awareness during surgical procedures under general anaesthesia. The influence of frontal brain tumours on bispectral index (BIS) measurements is unknown. The aim of our study was to determine whether BIS values recorded at loss and return of consciousness (LOC and ROC, respectively) differ between patients with unilateral frontal brain tumours and control patients.