Background: Diabetes mellitus (DM) is recognized as an important risk factor to tuberculosis (TB). However, there is significant diabetes under registration among tuberculosis cases which does not allow quantify the magnitude of this group. This study aims to determine the prevalence of DM among TB cases diagnosed in 2012 in Santiago de Chile, metropolitan area and to estimate the association of these two diseases. Method: A cross sectional study was undertaken. TB cases reported in the National Register of Tuberculosis were sought in the Information System for Management of Health Guarantees (SIGGES) to determine we ther or not they had be sides DM. The analysis of prevalence by age, sex and health service area was carried out, prevalence ratio was used to determine the level of association, and incidence rate of tuberculosis among diabetics and non-diabetics was estimated. Results: 23 TB cases were excluded for lack of necessary information, leaving a total of 821 cases. Prevalence of DM was 15.6% (13.2-18.2), with a prevalence ratio adjusted by age of 1.29 (1.28-1.29) respect to general population, and 1.73 (1.72-1.73) adjusted by sex. The estimated incidence rate of TB among diabetic population is 24.3 per 100,000, that is to say 1.7 times higher than general population of the region. Conclusions: Prevalence of DM in tuberculosis cases in Metropolitan Region was greater than in the general population. The study confirms that diabetics are a risk group for developing tuberculosis.