introduction. tuberculosis is an important cause of disease and death worldwide. an estimated 8.8 million new cases occurred in 2005 with 1.6 million deaths, including 195,000 among hiv-infected people. according to world health organization, the incidence rate was stable or in decline worldwide; however, the total number of new cases rose due to regional increases. anti-tb drug resistance is a significant public health problem and an obstacle for its control worldwide. therefore, measures must be taken for the adequate management of patients and the adoption of strategies to prevent tb dissemination. objective. the prevalence of resistance of mycobacterium tuberculosis was determined in untreated cases and in previously treated cases of pulmonary tuberculosis in colombia. materials and methods. a cross-sectional study determined the prevalence of resistance of mycobacterium tuberculosis to antituberculosis drugs in 1,189 untreated cases or previously treated cases of pulmonary tuberculosis between the years 2004 and 2005. cultures were collected throughout the country for this one-year period. drug susceptibility of the isolates was tested by the simplified variant of the cannetti, risk and grooset multiple proportions technique. results. the global resistance rate of 925 untreated patients was 11.8% (95% ci: 9-14%) and the rate of multidrug-resistant tuberculosis was 2.4% (95% ci: 1.6-3.6%). among 264 previously treated patients, the rate of global resistance was 44.3% (95% ci: 38-50%) and that of multidrug resistance was 31.4% (95%ci: 26-37%). conclusions. when compared to previous studies, these data show that there has not been a significant increase in drug resistance. the findings indicate that the current treatment scheme provided by the national tuberculosis program is adequate.