Background. Recently, world health organization (WHO) and the International Union Against TB and Lung Disease (Union) have acknowledged the need for international guidelines on the joint management and control of pulmonary tuberculosis (PTB) and diabetes mellitus (DM) and have published a provisional collaborative framework for the care and control of both diseases. This study aimed to determine the effect of DM on clinical manifestations and treatment outcome of PTB Methods. We conducted a retrospective study of patient with TB from 2009 to 2014 in Kyung Hee University hospital at Gangdong. The clinical manifestations and treatment outcome of 49 patients with DM (PTB with DM group) were compared to 226 patients without DM (PTB without DM group).Results. PTB with DM patients were older (66.1±15.7 vs. 52.15±19.8), had great body mass index (BMI) (22.4±3.2 vs. 20.9±2.9) and showed high frequencies of cavity on chest radiograph (OR=2.29, p=0.039). PTM with DM patients had delayed sputum conversion on 2 months (22.7% vs. 7.8%), a higher probability of unfavorable outcome (OR=2.91, p=0.005). Furthermore, DM, age, and bilateral infiltration on chest radiograph were factors independently associated with unfavorable outcome. Conclusion. DM seems to have a negative effect on clinical manifestations and treatment outcome on PTB.