Being a significant source of tuberculosis (TB) spread and the factor adversely affecting its epidemiological parameters, the relapses of TB remain a relevant problem. Aim: to establish the causes of pulmonary TB relapse (PTBR) and to evaluate its significance. Materials and methods – 80 phthisiologists have been interviewed using a special PTBR questionnaire. According to the results, the causes were divided into medical, organizational and social ones. Statistical analysis determined the degree of their significance (low, medium, high). Results. The most significant medical causes of PTBR were inadequate treatment, immunodeficiency, HIV infection, comorbidities, advanced TB, extensive residual lesions, drug adverse reactions. The organizational causes included low coverage of the population with fluorography, lack of follow-up, active detection and prophylaxis of cases in groups of risk, financial and infrastructure difficulties, poor medical-social support and population TB awareness, lack of fast diagnostics, poor management of comorbidities, lack of closed-type hospitals, stigma of TB patients, imperfect legislative base. The list of social causes consisted of low compliance to therapy, poor living and working conditions, low sanitary culture, migration of population and low social support. Among the significant (1-3 ratings) of social causes of RTBL respondents are: interrupted treatment (91,2 %), low commitment to treatment (83,7 %) and poor working conditions (71,2 %); p <0.05, among the average significant-unsatisfactory financial conditions, stay in prison and unemployment (65,0–35,0 %); p > 0,05, among others – careless attitude to one’s own health, low sanitary culture of the population, loneliness, low informative level of social institutions, migration of the population, homelessness, bad habits, poor nutrition, stress. Conclusions. The most significant medical factors of RTB development are: inadequate treatment of TB, immunodeficiency states, HIV infection, concomitant diseases, abandoned TB, major residual changes, side effects of medicines; organizational: low coverage of fluorography, lack of dispensary and active detection and prevention of TB in risk groups, financial and infrastructure difficulties, insufficient medical and social support, inaccessibility of rapid diagnosis absence of closed-type hospitals, stigma patients with TB, imperfect legislative framework; social: the disadvantage of treatment, unsatisfactory social and living conditions, low sanitary culture, population migration, social insecurity. Since the most threatening causes of PTBR were the limitations with the treatment of the newly detected TB cases we proposed considering “completion of the treatment course” as a conditionally effective treatment outcome and continue follow-up until final cure confirmation. Identifying a significant number of organizational limitations, as indicated by phthisiologists, raises the doubts about the transfer of out-patient management and follow-up of TB risk groups patients to primary care practitioners, who are not ready for this, mainly psychologically, and refusing from follow-up of newly detected TB and a significant reduction of the TB service. We believe that it would be advisable to restore dispensary follow-up (1 to 5 years) in the presence of such risks of PTBR as the extensive residual lesions, various immunodeficiency states, severe concomitant diseases and HIV infection. A considerable number of social factors for PTBR, aggravated by current war, will lead to a deterioration of the epidemic situation with TB, including the increase in the number of PTBR. In order to prevent a significant deterioration of the epidemiological situation with TB due to PTBR, we plan to develop the preventive organizational measures. Key words: tuberculosis, relapses, causes, questionnaires.