Cognitive impairment in patients with major cognitive impairment is often accompanied by behavioral and mental violations (BMV). BMV is common in both patients with major neurodegenerative cognitive impairment due to Alzheimer’s disease (MNDCI) and patients with major vascular cognitive impairment (MVCI). As cognitive impairment progresses, there is a gradual loss of basic activities in daily life such as feeding, dressing, bathing and movement, which are necessary for independent functioning. The article considers behavioral and psychoneurological symptoms and evaluates the functional activity in everyday life in patients with major cognitive impairment of various etiologies. To make a comparative characterization of the prevalence of behavioral and psychoneurologicall symptoms and to assess the functional activity in everyday life in patients with major cognitive impairment of various etiologies. Psychoneurological symptoms in patients with major cognitive impairment were quite heterogeneous and differed in structure and frequency of manifestations. Behavioral disorders in the vast majority of cases were significantly more common in patients MVCI (73.3 %) than MNDCI (36.7 %), p = 0.0040. Affective disorders (depressive) were also observed more often in patients with MVCI (67.8 %) than with MNDCI (38.2 %), p = 0.0370. When assessing the prevalence of psychoneurological symptoms on the NPI scale in patients with MVCI with the same severity, more pronounced depression/dysphoria (p = 0.0281), apathy/indifference (p = 0.0412) were noted. In patients with MNDCI, sleep and nocturnal behavioral disorders (p = 0.0389), irritability/mood lability (p = 0.0480). When assessing activity in daily life on the BADLS scale, no significant differences were observed in the total number of points in patients with MNDCI and MVCI (14,6 ± 3,35), (19,0 ± 4,06), р = 0,3961. However, an important feature of the comparative characteristics of the functional status in MNDCI and MVCI in mild disease severity were the presence of more significant and probable differences in subtests: «ability to shop» (p = 0.0047), «time orientation» (p = 0.0242), «cooking» p = 0.0335), «use of transport» (p = 0.0439). In patients with MVCI moderate degree by subtests: «dressing» (p = 0.0035), «time orientation» (p = 0.0421), «walking» (p = 0.0473). Thus, according to the results of the study, patients with MVCI had more serious behavioral, psychoneurological symptoms and functional disorders than patients with MNDCI.