Lewy body dementia (LBD) is a progressive brain disease manifest as dementia and parkinsonism, along with psychotic and autonomic disorders. Although studies in recent years have demonstrated the positive effects of cholinesterase inhibitors in LBD, the search for therapeutic agents with other mechanisms of action remains relevant. An open, controlled, 16-week study was performed with the aim of evaluating the efficacy and safety of memantine in patients with clinically diagnosed LBD (criteria of McKeith et al., 1999). The study included 23 patients (mean age 69.2 +/- 5.9 years), who were divided into two groups: 14 patients received memantine at a dose of 20 mg/day and nine patients constituted the control group. Efficacy was evaluated using a battery of quantitative neurospychological tests, clinical scales for assessment of fluctuations in mental states, scales for assessment of behavioral and psychotic disorders, and the general clinical impression scale. The results demonstrated that memantine had positive effects on the patients' general status and cognitive functions (increases on the mini mental state examination by 1.5 points), mainly because of improvements in attention and control functions. There were also reductions in the severity of fluctuations in mental state, aggressivity, lack of spontaneity, and disinhibition. The severity of psychotic and motor disorders did not change significantly. Tolerance of the agent was good, only two patients withdrawing from the study because of episodes of confusion during the dose titration period.