AbstractTuberculosis (TB) is the leading cause of death among infectious diseases worldwide. Among the estimated cases of drug-resistant TB, approximately 60% occur in the BRICS countries (Brazil, Russia, India, China and South Africa). Among Brazilian states, primary and acquired multidrug-resistant TB (MDR-TB) rates were the highest in Rio Grande do Sul (RS). This study aimed to perform molecular characterisation of MDR-TB in the State of RS, a high-burden Brazilian state. We performed molecular characterisation of MDR-TB cases in RS, defined by drug susceptibility testing, using 131Mycobacterium tuberculosis (M.tb)DNA samples from the Central Laboratory. We carried out MIRU-VNTR 24loci, spoligotyping, sequencing of thekatG,inhA andrpoB genes and RD^Riosublineage identification. The most frequent families found were LAM (65.6%) and Haarlem (22.1%). RD^Riodeletion was observed in 42 (32%) of theM.tbisolates. Among MDR-TB cases, eight (6.1%) did not present mutations in the studied genes. In 116 (88.5%)M.tbisolates, we found mutations associated with rifampicin (RIF) resistance inrpoB gene, and in 112 isolates (85.5%), we observed mutations related to isoniazid resistance inkatG andinhA genes. An insertion of 12 nucleotides (CCAGAACAACCC) at the 516 codon in therpoB gene, possibly responsible for a decreased interaction of RIF and RNA polymerase, was found in 19/131 of the isolates, belonging mostly to LAM and Haarlem families. These results enable a better understanding of the dynamics of transmission and evolution of MDR-TB in the region.