<sec id="st1"> <title>SETTING</title> The prevalence of diabetes mellitus (DM) worldwide is increasing markedly, and many countries with rising rates also have a high incidence rate of tuberculosis (TB). </sec> <sec id="st2"> <title>OBJECTIVE</title> To investigate the relationships of fasting serum glucose (FSG) and DM with TB incidence, recurrence and mortality risk in a prospective cohort study in South Korea. </sec> <sec id="st3"> <title>DESIGN</title> Our study comprised 1 267 564 Koreans who received health insurance from the National Health Insurance System, had an initial medical evaluation between 1997 and 2000 and were prospectively followed biennially. </sec> <sec id="st4"> <title>RESULTS</title> Participants with DM had a higher risk for incident TB (hazard ratio [HR] 1.81, 95%CI 1.71-1.91 in males, HR 1.33; 95%CI 1.20-1.47 in females) than those without DM. There was a strong positive trend for TB risk with rising FSG among males. The risk for recurrent TB among those with previous TB was significantly higher in males (HR 1.58, 95%CI 1.43-1.75) and in females with DM (HR 1.38, 95%CI 1.08-1.76). The increased risk of death from TB during follow-up was also significant in men (HR 1.91, 95%CI 1.87-1.95) and in women (HR 1.71, 95%CI 1.65-1.77). </sec> <sec id="st5"> <title>CONCLUSIONS</title> A diagnosis of DM is a risk factor for TB, TB recurrence and death from TB. Screening for TB should be considered among people living with DM in Korea, particularly those with severe DM. </sec>.