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). 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. 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. 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). 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.