BACKGROUND: Tuberculosis (TB) is a bacterial infection that usually affects the lungs, although it can also affect other parts of the body. Vitamin D deficiency and response to treatment have been demonstrated in patients with active TB in several studies, but not in MDR-TB patients, which is a new observation in the present study. OBJECTIVE: To study the time to initial sputum culture conversion and to associate baseline vitamin D levels and response to treatment in patients with PTB Cat I and MDR-TB. METHODS: A total of 897 North Indian participants were recruited and divided into three groups: treatment-naïve PTB Cat I, MDR-TB, and healthy controls. Serum biochemistry, including 25-hydroxyvitamin D and calcium, was measured in all participants with PTB, Cat I, and MDR-TB. RESULTS: PTB Cat I patients had high bacillary load grading at baseline compared to 2 month followed by 6 month of treatment. More severe chest radiographic features, such as cavitation and the presence of bilateral disease at baseline. Mean sputum smear conversion times were 0.95 ± 0.7 months and culture conversion to negative occurred at a mean time of 0.8 ± 0.7 in PTB Cat I patients compared to MDR-TB patients on average sputum smear and time of 2.4 ± 3 months. Significantly lower mean serum 25-hyroxyvitamin D concentration was found in the 6 month than in the 2 month and baseline in PTB Cat I. CONCLUSION: Low serum vitamin D deficiency was observed in both groups during treatment and is one of the important factors responsible for susceptibility to TB in both groups; however, its significance is uncertain. Patients with continuous positive sputum for multidrug-resistant tuberculosis (MDR-TB) had a worse prognosis than those with sputum bacteriology conversion. Two months into a treatment regimen, sputum smear conversions may be a useful indicator of an MDR-TB patient's prognosis.