Co-infection with HIV and Mycobacterium tuberculosis is common, particularly in the developing world. Tuberculosis (TB) is the commonest co-infection in HIV-positive individuals, who are at increased risk of both reactivation of latent infection and acquisition of new infection. As the degree of immunosuppression increases, the risks of developing TB disease also increase. The patho-physiology, clinical picture, differential diagnosis and diagnostic tests are discussed, together with the interactions between antiretroviral therapy and anti-tuberculous chemotherapy. Indications for chemoprophylaxis and vaccination against TB are reviewed.