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In Bulgaria during 2007-2011, a total of 188 MDR/ XDR M. tuberculosis isolates were characterized by drug- susceptibility testing and spoligotyping (31 in 2007, 31 in 2008, 39 in 2009, 47 in 2010, and 40 in 2011) and represent 72% of the 261 MDR/XDR M. tuberculosis isolates identi- fied during that period. The MDR/XDR strains were iso- lated from sputum of 181 (96.2%) patients, gastric lavage fluid from 3 (1.5%), bronchoalveolar lavage fluid from 2 (1%), pleural fluid from 1 (0.5%), and fistula swab sample from 1 (0.5%). The first MDR/XDR M. tuberculosis strain isolated per patient was analyzed for this study. Drug susceptibility of these strains was confirmed by the National Reference TB Laboratory, which used liq- uid culture at concentrations of 0.1 µg/mL for isoniazid, 1 µg/mL for rifampin, 5 µg/mL for ethambutol, 1 µg/mL for streptomycin, 2.5 µg/mL for capreomycin, 1 µg/mL for amikacin, 5 µg/mL for kanamycin, and 2 µg/mL for ofloxacin. Of the MDR/XDR strains, 77 (41%) were resis- tant to all first-line anti-TB drugs, 51 (27%) were resistant to isoniazid and rifampin; 38 (20%) to isoniazid, rifampin, and streptomycin; and 22 (12%) to isoniazid, rifampin, and ethambutol. Second-line drug-susceptibility testing was performed for 174 (81%) of the MDR strains. Of these, 140 (80%) were sensitive to all second-line anti-TB drugs and 20 (12%) were resistant to ofloxacin. Five percent (n = 9) of XDR strains had combined resistance to ofloxacin, ami - kacin, kanamycin, and capreomycin. To detect and genotype the Beijing strains, we used a spoligotyping kit (Isogen Bioscience BV, Maarssen, the Netherlands), and we performed single-nucleotide polymorphism typing by bead-based multiplex ligation- dependent probe amplification (MLPA) (8,9). We also screened for the presence of the Beijing genotype in 117 drug-sensitive strains collected from across the country in 2011, representing a convenience sample of ≈10%. Both methods identified 1 drug-sensitive M. tuberculosis strain