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Background and Aims According to the literature, deep sedation may be associated with significant neurocognitive dysfunction postoperatively. The aim of the study was to compare the impact of sedation depth monitoring according to BIS versus clinical assessment on neurocognitive function in elderly patients undergoing spinal anesthesia with sedation.Methods The study was approved by the Local Kauno Regional Ethic Committee (Nr. BE-2–53). Elderly patients (>65 years old) scheduled for elective knee arthroplasty under spinal anesthesia with sedation were included in the study. Patients were randomly assigned into two groups. In the first group (BIS group), sedation was administered according on BIS value (targeting 70–80, light sedation). In the control group (non-BIS group), sedation was guided only by clinical signs (standard clinical practice, Ramsay sedation scale 4). For procedural sedation continuous infusion of propofol was performed according to the group. The neuropsychological testing was performed using Addenbrooke’s Cognitive Examination – Revised (ACE-R) test. Cognitive assessments were performed four times: preoperatively (preOP) and at 2, 30, and 90 days postoperatively (2 POD, 30 POD, 90 POD respectively). Results are presented as median with minimum and maximum values.Results Total number of 60 patients aged over 65 were enrolled in this study. There were no statistically significant differences between two groups ACE-R scores at all time points: preOP BIS group 88 (73–96) vs. non-BIS 86 (48–95), p=0.142; 2 POD BIS group 91.5 (73–99) vs. non-BIS 88.5 (48–99); p=0.052; 30 POD BIS group 93 (66–98) vs. non-BIS 90 (45–97), p=0.064; 90 POD BIS group 92 (77–97) vs. non-BIS 92 (46–99), p=0.951.Conclusions In our study we do not found differences in neurocognitive function between two sedation depth monitoring methods (sedation depth monitoring according to BIS versus clinical assessment) in elderly patients undergoing spinal anesthesia with sedation. More studies with larger sample size are needed.