Introduction. The processes of comparing post-mortem clinical and pathoanatomic diagnoses, determining the categories of their discrepancies currently belong to the area of responsibility of the medical commission of a medical organization. The modern scientific literature and the normative field have not defined a scientifically based methodology for comparing diagnoses and determining the category of their discrepancy. The creation and implementation of such an approach will solve one of the most important problems for practicing doctors and health care organizers. The purpose of the study is to develop a methodology for comparing post-mortem and pathoanatomic diagnoses by the medical commission of a medical organization. Materials and methods. Within the framework of a retrospective cohort study, 8269 cases of providing medical care with a fatal outcome in therapeutic pathology were analyzed, for which an examination was carried out within the framework of mandatory medical insurance. The analysis of cases was carried out for the correctness of the formulation of the post-mortem clinical diagnosis and the results of its comparison with the pathoanatomic diagnosis based on the results of the examination of the quality of medical care in compulsory medical insurance. Results. Using the method of clinical and anatomical parallels, the differences between postmortem and pathoanatomic diagnosis are formulated. At the second stage, the significance of the identified nonconformities is assessed (which nonconformities are subject to further assessment). At the third stage, the presence of a discrepancy in the main (competing, combined) diseases was determined. At the fourth stage, external and internal objective factors that affect the activities of a medical organization and did not allow to establish a diagnosis are identified. To establish the category of discrepancy between postmortem and pathoanatomic diagnoses, the role of violations in the provision of medical care in the formation of a fatal outcome (the severity of the underlying disease (and its complications); the initial state of the patient's body; medical care) is determined. The parameters of assessing the severity of pathology and the effectiveness of medical technology are conditionally identified and the degree of influence of violations in the provision of medical care on the formation of unfavorable outcomes according to the method of S. Kulbak is mathematically estimated. The influence of several violations on the formation of unfavorable outcomes was assessed using the indicator of accumulated informativeness (Jn). Discussions. The method allows us to identify a significantly greater number of discrepancies in post-mortem and pathoanatomic diagnoses, similarly, the number of discrepancies in all categories is significantly more detected. The result of applying the proposed methodology by different experts in the same case is repeatable in 95% of cases. Conclusions (conclusion). An original method of comparing postmortem and pathoanatomic diagnoses, determining the category of their discrepancy, is proposed. During the testing, the method showed its effectiveness and objectivity. The technique can be recommended for use in the work of medical commissions of medical organizations (for the study of fatal outcomes).