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TOBACCO USE is among the leading preventable causes of death worldwide,1 and is a major contributor to respiratory diseases, including tuberculosis (TB).2 Smoking reduces normal mucociliary clearance of tracheobronchial secretions and impairs alveolar macrophage function against Mycobacterium tuberculosis.3 Culture conversion to negative after the first 2 months of treatment is a widely used measure of bacteriologic response to therapy in anti-tuberculosis treatment trials, and is associated with long-term cure.4 Delayed sputum conversion prolongs the time during which patients are infectious and capable of transmitting TB to others in their community. Several studies have examined the impact of smoking on sputum smear and culture conversion and outcomes of TB treatment.2 Smoking did not affect smear conversion in a study from Kuwait,5 whereas smoking and bilateral cavitary disease increased the risk of culture positivity two fold after the first 2 months of treatment in a cohort of non-human immunodeficiency virus (HIV) infected patients with drug-susceptible TB in Spain.6 Batista et al. recently reported that smoking was associated with a 2.5-fold increased risk of relapse after treatment in 754 patients in Brazil.7 However, most earlier studies did not control for confounding by other factors associated with delayed response to treatment, such as non-adherence to treatment, alcohol use and cavitary disease.8 To further examine the impact of smoking and other factors on bacillary clearance and response to anti-tuberculosis treatment, we analyzed sputum culture status during the first 2 months of treatment in adults with non-cavitary pulmonary TB participating in a TB treatment trial.