The aim of this randomized, double-blind, placebo-controlled 16-week study was to investigate the clinical efficacy of cyclandelate (Natil®, 1,600 mg/day) in 139 adult outpatients with cognitive impairment (70 allocated to cyclandelate; 69 to placebo). Quantitative-topological EEG, event-related potentials (P300) and psychophysiological interview-based rating scales were used. The efficacy of cyclandelate was demonstrated in the confirmatory statistical sense using a global Hailperin-Rüger test on 10 predefined primary variables at global significance level of 0.05 relating to psychopathology, psychometry, neuropsychophysiology and behavior. At psychopathological and behavioral level the reduction of the total scores of the rating scales (Alzheimer Disease Assessment Scale, Sandoz Clinical Assessment Geriatric Scale, and Nürnberger Selbsteinschätzungs-Liste) following a 16-week therapy revealed also an individual significant cyclandelate-placebo distinction in the confirmatory statistical sense. A difference between verum and placebo was also observed by the increase of the number of correct answers during performance of the number symbol test (psychometrical level). The objective electrophysiological data (neuropsychophysiological level) support these findings. Of particular interest is that following cyclandelate treatment the absolute theta power remained almost unchanged and an increase of P300 amplitude was observed. At the same time placebo led to a distinct theta power increase and a decrease of P30o amplitude, which was interpreted as the reflection of an impairment of the initial clinical state. Summarizing, cyclandelate proved to be efficacious compared to placebo in patients with mild to moderate cognitive impairm