Worldwide elimination of tuberculosis, which was near to becoming a reality, is seriously threatened by the HIV epidemic, particularly in Africa. In countries with high prevalence of both HIV and TB, new smear-positive, smear-negative and extra-pulmonary TB cases are increasing. Estimates of the prevalence of HIV are unavailable, although they can be guessed from the reported prevalence of AIDS and the approximate ratio of HIV infections to AIDS of 25. The prevalence of TB has fallen about 10-14% yearly or 50% every 5-7 years in developed countries. For example in the Netherlands, TB prevalence is 0.4% in people 20 and 12% in those 50. The low prevalence of TB in young adults in developed countries suggests that HIV will have virtually no influence on the elimination of TB in these countries. In developing countries, however, annual decrease in TB has been very low, about 1-2% during the last 4 decades. The prevalence of TB in young adults is similar to that found by WHO surveys in the 1950s, 50%. It is possible that the absolute number of TB cases will increase as AIDS becomes a problem. Most of the new cases will originate from reactivation of latent infections in AIDS cases, but some will be new active infections. Such an increase in cases has already been seen in Tanzania and Malawi in 1988. 43% more smear-positive cases were reported in Malawi, due to HIV infection and to influx of Mozambican refugees. The current level and the risk of TB infection and its trend are the most decisive factors controlling the epidemiology of TB and HIV in the future.