The article describes the use of mathematical modeling methods for calculating the weight coefficients of predictors of mortality in patients with HIV / tuberculosis - co-infection, from among persons held in institutions of the penitentiary system. The development of prognosis models is important for fulfilling the tasks of preventing the occurrence of infectious diseases, improving the quality of medical care, timely correction of treatment tactics, and improving organizational measures. The aim of the study was to identify the most significant predictive factors of an unfavorable outcome of HIV / tuberculosis-coinfection in persons held in penitentiary institutions. The material for the study was the data from a retrospective analysis of case histories of patients with HIV / tuberculosis co-infection (246 people) who were hospitalized in a specialized institution of the penitentiary system from 2012 to 2016. The analyzed predictive factors of an unfavorable outcome were established by the method of optimal-reliable partitions of the attribute space described at the previous stage of the study. The assessment of the influence of predictors on the adverse outcome was carried out on the basis of data from a survey of expert doctors from the Medical Sanitary Unit of the Federal Penitentiary Service of the Udmurt Republic (7 experts participated). The method of research was the logical-mathematical method of analyzing hierarchies, which consists in breaking the non-formalizable problem into simple components by constructing a circuit in the form of an inverted tree. At the top is the goal of the study or the problem under study. Results. It was found that the prognostically unfavorable factors that have the greatest impact on the unfavorable prognosis of HIV-associated tuberculosis were the presence of active HIV-associated diseases, extensive and chronic forms of the tuberculosis process, low CD 4 lymphocytes (less than 88 cells / ml), high viral load HIV (Above 600,000), heart rhythm disorders