Tuberculosis is a major cause of morbidity and mortality in developing countries. It is estimated that one-fifth of the world population is infected, 12-16 million people have the disease, every year 6-8 million develop tuberculosis and 2-3 million die from it. Four methods for the prevention of tuberculosis are available: improvement of socio-economic conditions, case-finding and treatment, chemoprophylaxis, and vaccination. Each of these methods is examined in relation to a model of the chain of transmission and development of disease. Improvement of socio-economic conditions, responsible for the decline of tuberculosis in the developed world, must be seen as a long-term solution. Case-finding and treatment is the only method expected to have an important short-term impact on transmission. A summary of the results of 35 studies shows the estimated efficacy of bacillus Calmette-Guérin (BCG) vaccination ranging from 96% to none. Follow-up results from 10 controlled trials are consistent with waning of BCG protective efficacy with time since vaccination. Chemoprophylaxis and vaccination are expected to protect the individual but not to have a significant short-term impact on transmission.