Background and Objectives: Although vitamin D is implicated in the generation of anti-microbial peptide cathelicidin, which plays a key role against pulmonary tuberculosis (PTB), and may have an inverse association with the risk of type 2 diabetes (DM), its role in the co-existence of these two diseases (PTB-DM) is still uncertain. This study explored the association of vitamin D status with prevalent PTB, PTB-DM and DM. Methods and Study Design: We randomly selected 130 PTB patients, 90 PTB-DM, 91 DM and 134 controls. Serum 25(OH)D was determined. A structured questionnaire and anthropometric measurements were administered. Results: Serum 25(OH)D in PTB and PTB-DM were 12.2±2.2 ng/mL and 12.9±2.5 ng/mL, respectively, which were lower than those in DM and control groups. Odds ratios of PTB and PTB-DM comparing extreme quartiles of 25(OH)D (lower than 8.6 ng/mL versus ≥26.6 ng/mL) were 3.26 and 2.27, respectively. These associations remained after adjustment for possible risk factors [OR (95% CI)=4.73 (2.04-10.9) and 2.50 (1.04-6.02), respectively]. A synergistic interaction was observed between low 25(OH)D and underweight in respect to prevalent PTB-DM [OR=24.6 vs 2.50 for lowest quartile of 25(OH) D and 4.59 for underweight]. Conclusions: Odds ratios of low serum 25(OH)D for PTB and PTB-DM were greater than 1.0, and were even much greater when combined with underweight. However, since the association of serum 25(OH)D with PTB was stronger than with PTB-DM, we could not draw the conclusion that vitamin D is a link between PTB and DM.