The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) replaces the term «dementia» with «major neurocognitive disorder» (MNCD), which can reduce the  stigmatization of patients and focus the attention of specialists on  the preserved abilities of patients rather than deficit symptoms. In  the next 35 years, the number of patients with MNCD in the world is  predicted to almost triple. The article considers the concept,  epidemiology, and etiological pattern of this syndrome. It  characterizes in detail Alzheimer's disease (AD) that is a cause of  MNCD in 50–70% of cases. The current diagnostic criteria and  clinical presentations of the disease are given. The presence of early and significant episodic memory disorders as both alone or  concurrent with other cognitive and behavioral changes reflects the  main clinical phenotype of AD. Magnetic resonance morphometry,  amyloid positron emission tomography, and estimation of  cerebrospinal fluid β-amyloid and tau protein levels find increasing  applications in research and routine practice. Drug and non-drug  treatments for MNCD are considered. The use of akatinol memantine to treat this disorder and the issues related to the comprehensive management of patients with severe cognitive impairment are analyzed.