This prospective study was designed to evaluate the correlation between the electroencephalographic bispectral index (BIS) and the hypnotic component of anaesthesia (CA) induced by sevoflurane in 27 children and 27 adult patients. BIS and CA were compared at loss of consciousness (LOC) and on recovery of consciousness (ROC). Mean (SD) BIS decreased significantly at LOC in children and adults from 94 (2.7) to 87.4 (4) and from 96.2 (2) to 86.7 (4.4), respectively, without any difference between groups. Correlation coefficients (p) between BIS and CA at LOC were -0.761 in children and -0.911 in adults. BIS increased significantly at ROC in children and adults from 74.1 (4.2) to 86.7 (2) and from 80.2 (5) to 90.7 (3), respectively, without any difference between groups. Correlation coefficients between BIS and CA in ROC were -0.876 in children and -0.837 in adults. BIS values at ROC were not different from those at LOC in either group. These data demonstrate that BIS correlates with the hypnotic component of anaesthesia induced by sevoflurane in children as well as in adults.