BACKGROUND Bispectral index (BIS) monitoring can reduce the duration of anesthesia. This study aimed to evaluate the effects of BIS monitoring during surgery for resection of colon carcinoma in elderly patients using the Attention Network Test (ANT) to study alerting, orienting, and executive functions, and the Confusion Assessment Method (CAM). MATERIAL AND METHODS Eighty-one patients (65-75 years) underwent radical surgery for colon carcinoma with general intravenous anesthesia, propofol (6-8 mg/kg/h), vecuronium (0.03-0.05 mg/kg/min), and remifentanil (0.1-0.2 μg/kg/min). The BIS group (n=41) underwent adjustment of anesthesia to maintain a BIS value between 40-60; the non-BIS group (N=40) underwent standard intraoperative hemodynamic monitoring. Primary endpoints were alerting, orienting, and executive functions assessed pre-operatively and on postoperative days 1 and 5 using the ANT; the secondary endpoint was delirium during the first five postoperative days, assessed using the CAM. RESULTS Propofol and remifentanil doses were significantly lower in the BIS group compared with the non-BIS group (P<0.001). Alerting, orienting, and executive functions showed no differences between the two groups pre-operatively but were impaired in both groups on postoperative day 1 compared with pre-operative levels (P<0.001). On postoperative day 5, alerting (P=0.607) and orienting (P=0.851) functions recovered in the BIS group but remained impaired in the non-BIS group (P<0.001). Delirium was significantly lower in the BIS group compared with the non-BIS group (17.5% vs. 27.5%) (P<0.001). CONCLUSIONS BIS-guided anesthesia was associated with reduced anesthetic exposure, early postoperative recovery of alerting and orienting functions, and reduced postoperative delirium.