Background: Unintended intra-operative awareness is a serious complication of general anesthesia. The incidence of such awareness has been reported to be about 0.1-0.6% of patients under general anesthesia. Reminiscence of what occurred during the operation can be felt by patients, which can be stressful and leave lasting mental suffering afterward the operation. Patients that experience unintended intra-operative awareness may have some combination of auditory function, tactual feeling, a sense of weakness, an inability to move, pain, and dread. Bispectral Index (BIS) monitoring has been shown to decrease awareness and boost recovery time from anesthesia. Aims of the study is to evaluate the clinical impact of BIS monitoring to reduce the incidence of awareness and its impact on hemodynamic parameters, drug consumption, the recovery time and the end-tidal concentration of volatile anesthetics in adult patients undergoing various types of surgery under general anesthesia.