Purpose: to study the follow-up period of a patient who completed the follow-up with a fatal outcome from the corresponding condition in areas with low population density. Methods: in a multicenter (Kamchatsky Krai, Magadan region) uncontrolled study, the life expectancy of people who died from HIV (159 cases), tuberculosis (170 cases) and viral hepatitis B and C (30 cases) was analyzed. Results: Median survival in patients with HIV disease is 2.5 years (25% quartile 0.8 years, 75% quartile 6 years). Survival is described as 104.42 x e-0.212 x year from the detection of infection. The life expectancy of women was less than that of men. The proportion of deaths from tuberculosis among all deaths from tuberculosis is highest in the first year (36.9%), when patients die mainly from generalized and acutely progressive forms. In subsequent years, the proportion of fibrous-cavernous tuberculosis increases; the maximum proportion of deaths from all deaths is observed in the third year (12.5%; 95%CI 30.7-45.1). The median survival of patients who ultimately die is 1.2 years. Women die at a shorter time than men. The majority of patients who died from viral hepatitis (56.7%; 95% CI 39.2-72.6) died in the second year of the disease. Conclusion. When planning studies related to the survival of patients with HIV infection, it is advisable to use pro- or retrospective studies of survival analysis with a follow-up period of more than a median survival of 2.5 years (optimally - more than 6 years). The planning of mortality studies in patients with tuberculosis is associated with two periods: early mortality associated with acutely progressive and disseminated forms of tuberculosis can be studied on an annual cohort. With regard to late mortality, it should be studied on a cohort followed up for five years, not including patients who died during the first year of life. To study mortality caused directly by viral hepatitis, it is necessary to use a cohort with a follow-up period of at least three years. Exponential models can be used in the analysis of survival in diseases caused by HIV, tuberculosis, and parenteral viral hepatitis.