Aim — to determine the incidence of QT interval prolongation (QTP) in patients receiving antituberculous chemotherapy. Material and methods. There were 126 patients with active tuberculosis for the period from May 2016 to June 2017 who received antituberculosis chemotherapy. Four drugs were administered within antituberculous medication on the average (range 1—6). Annotated impersonal single-channel electrocardiograms (duration 5 min) by using of CardioQVARK monitor were made in all patients. Corrected QT interval (QTc) was calculated according to the Bazett’s formula (for heart rate 60—100) or to the Frederick’s formula (heart rate less than 60 or more than 100). QTc over 450 ms for men and over 470 ms for women were considered as QTP. Results. The QTP (476 ms (460,5; 489,5) was revealed in 117 (12,2%) cases from 958 ECGs among 41 (32.5%) patients. In 116 (92%) cases, at least one drug affecting QT interval duration was included in the therapy (anti-tuberculosis or concomitant). Among them there were drugs with known (in 81.7%) and possible (in 25.4%) risk of torsades de pointes (TdP). In patients with QTP, there were more frequent cases of fibro-cavernous tuberculosis and caseous pneumonia (p=0.018), active bacteria discharge (p=0.046) and smoking (p=0.022). Also, patients with QTP took more drugs affecting QT interval duration (p=0.005) including medicines with known (p=0.015) and possible (p=0.023) risk of TdP. Conclusion. Widespread QTP was observed in patients receiving antituberculous chemotherapy. Regular ECG monitoring is necessary to control the safety of treatment.