Tuberculosis (TB) and diabetes mellitus (DM) are major global health problem. Although the incidence of tuberculosis has declined in high-income countries, it remains still high in South Korea. At the same time, the prevalence of DM is increasing. Therefore, it is important to know about the relationship between DM and TB. There is growing evidence that DM is an important risk factor for TB and might affect disease presentation and treatment response. A systematic review found a relative risk of 3.1 for TB disease among persons with DM compared with persons who did not have DM. In addition, diabetic populations show more severe presentations than non-diabetic populations. Several studies evaluated the manifestations and outcomes of TB in diabetic populations. And, they found that diabetic populations have higher smear positive rate, more cavities and higher rates of treatment failure than non-diabetics. Impairment of host defense plays an important role for these presentations and treatment outcome in diabetic patients. It is also reported that the severity of tuberculosis depends on the degree of hyperglycemia. Therefore, glucose control is also important for the TB control.