Since the mid-1980s, the rate of decline in reported cases of tuberculosis (TB) has reached a plateau or reversed because of a combination of poverty and increased homelessness, immigration and displacement, poorly managed and supplied TB control programmes and, particularly in the developing world, the emergence of human immunodeficiency virus (HIV) infection. TB in HIV-positive patients may present atypically, both clinically and radiologically, with a lower probability of sputum positivity, greater difficulty in diagnosis, and a more rapid clinical deterioration than TB in HIV-seronegative patients. The emergence of multiple-drug-resistant strains of Mycobacterium tuberculosis, particularly in patients infected by HIV, carries a high mortality and has been associated with outbreaks in Europe and the USA. Microscopy and culture form the basis of diagnosis, but there is a need for more rapid diagnostic techniques and novel methods of drug susceptibility testing. Prolonged supervised treatment programmes and the development of new chemotherapeutic agents and regimens are essential prerequisites for successful TB therapy in AIDS patients. This review examines the clinical, microbiological and epidemiological issues associated with TB in HIV-infected individuals.