BACKGROUND: While previous studies have shown that cigarette smoking increases the infectiousness of tuberculosis patients, the impact of smoking cessation on tuberculosis transmissibility has not been evaluated. METHODS: Between 2009 and 2012, we enrolled 4500 tuberculosis patients and followed 14 044 household contacts in Lima, Peru. Tuberculosis patients were classified into 4 categories: never smoked, quit in the distant past (stopped smoking >2 months prior to time of diagnosis), recently quit (stopped smoking ≤2 months prior to time of diagnosis), and active smokers. We used a modified Poisson generalized estimating equation to assess the risk of tuberculosis infection of child contacts at enrollment and by 6 months of follow-up. RESULTS: In total, 1371 (76.8%) child contacts were exposed to patients who had never smoked, 211 (11.8%) were exposed to distant quitters, 155 (8.7%) were exposed to recent quitters, and 49 (2.7%) were exposed to active smokers. Compared with child contacts of index patients who had never smoked, child contacts of recent quitters had a similar risk of tuberculosis infection at enrollment (adjusted risk ratio, 95% confidence intervals [0.81, 0.50-1.32]) and by six months of follow-up (0.76, 0.51-1.13); and by 6 months of follow-up (aRR, 0.76; 95% CI, .51-1.13); child contacts of recent quitters had a significantly reduced risk of tuberculosis infection compared with contacts of active smokers (enrollment 0.45, 0.24-0.87; 6-month follow-up 0.48, 0.29-0.79). CONCLUSIONS: Our results show that the adverse effects of smoking on the transmissibility of tuberculosis are significantly reduced shortly after quitting smoking, reinforcing the importance of smoking cessation interventions in tuberculosis control.