The objective: to justify the optimal duration of chemotherapy with Lzd and Bdq by evaluating the long-term treatment outcomes in patients with multiple/pre-extensive drug resistant (MDR/preXDR) tuberculosis who interrupted treatment at different time points.Subjects and Methods. 800 patients with MDR/preXDR tuberculosis were enrolled in the study, they were from all regions of the Russian Federation and they started a course of chemotherapy with regimens containing Lzd and Bdq in 2017-2018. All patients who interrupted their chemotherapy (124) were divided at 4 groups. Group 1-43 patients who received less than 90 doses, Group 2-37 patients who received from 91 to 180 doses, Group 3-39 patients who received from 181 to 270 doses, and Group 4-5 patients who received from 271 to 360 doses of anti-tuberculosis drugs.Results. In Group 3, the effectiveness of reaching a favorable outcome during observation for 3-4 years made 53.8% in 21/39, which was comparable to the effectiveness of treatment with a 24-month course of chemotherapy (2017 – 58.0 and 2018 – 52.1%). The treatment duration of patients from Group 3 was additionally analyzed, the arithmetic mean of the number of administered doses makes 262 ± 15, which allowed recommending 9-month courses of chemotherapy.