There is increasing evidence of a link between tuberculosis and smoking. This paper reviews the epidemiological evidence from the UK, China, India and the USA, summarizing some of the main papers which indicate an association. Where an association has been found there seems to be an increase in tuberculosis case rates of between two- and four-fold for those smoking in excess of 20 cigarettes a day, but it may be difficult to control for other factors, particularly alcohol consumption. The final part of the paper reviews possible mechanisms. A likely possibility is that nicotine turns off the production of TNF-alpha by the macrophages in the lungs, rendering the patient more susceptible to the development of progressive disease from latent Mycobacterium tuberculosis infection.