
In a review of literature data and materials of our own research, we discuss some aspects of the urgent problem of clinical medicine – comorbidity. The aim of this work was to study modern concepts of polymorbidity and comorbidity in literature data. The terms that are used to refer to the combination of several diseases in one person are presented: «combined», «concomitant», «associated» diseases or conditions, «comorbid» diseases or conditions, «comorbidity», «polymorbidity», «multimorbidity», «multifactorial» diseases», «polypathy», «condolences», «double diagnosis», «pluripatology». Definitions are given for the currently most used terms «comorbidity», «polymorbidity» and «multimorbidity», as well as the historical aspects of their occurrence are considered. The differences between the concepts of «comorbidity» and «polymorbidity» are shown, despite their frequent use as synonyms. Existing classifications of comorbidity are considered, including the concepts of trans-systemic, transzological and chronological comorbidity. The classification developed by H.C. is shown. Kraemer and M. van den Akker (1998), which presents causal, complicated, iatrogenic, unspecified and random comorbidity. Scales for assessing this phenomenon are given: Cumulative illness rating scale, index Kaplan – Feinstein, Cumulative illness rating scale for geriatrics, Index of co-existent disease, Geriatric index of comorbidity, Functional comorbidity index, Total illness burden index. A more detailed assessment of comorbidity using the Charlson index as the most used and having the least drawbacks is presented. A description of the quantitative assessment of polymorbidity is given and the fluctuation of the number of diseases depending on the age of the person is shown. The list of the most common pathologies that can be combined in one patient is given. Diseases that are characteristic of elderly and senile patients are noted. The problem of comorbidity is becoming increasingly important in those countries and regions where the social conditions of society contribute to increasing the life expectancy of people of advanced and senile age, which indicates the need to develop a unified view of the problem of combined pathology.