The relevance of the study of mental disorders of late age is determined by modern socio-demographic conditions. The system approach makes it possible to clearly identify the structural components of severe cognitive disorders with the release of cognitive, psychopathological and socio-behavioral-functional disorders that make up a single dynamic symptom complex. Dimension ("measuring") approach to mental disorders contributes to the allocation of individual "objects" - painful for their scientific knowledge of the phenomena that on the one hand allows them to" measure " and rank, on the other hand, reduces the ability to assess the contribution to their occurrence of various factors and mechanisms. The article is presented in the genre of scientific discussion and actualizes epistemological problems in relation to mental disorders of late age.