A numeric value derived from bispectral analysis of EEG, the bispectral index (BIS), has been recently introduced as a monitor of the hypnotic component of anaesthesia. Application of BIS monitoring in anaesthesia appears extremely interesting to drugs titration and drugs economy, and in the evaluation of time for discharge in a one day surgery regimen. In this prospective study ASA I-II patients for Day-Surgery were enrolled in three groups: subaracnoid anaesthesia (SA), general anaesthesia (GA) with BIS and GA without BIS monitoring. At present 35 patients for DS operative hysteroscopy were enrolled. No significant differences were measured between the GA groups. A longer time of recovery was necessary in the SA group. A greater amount of anaesthetic in BIS group could be attributed to a better monitoring of sedation which prevents intraoperative awakening.