The earliest reports of the acquired immunodeficiency syndrome (AIDS) in homosexual men in the United States¹ included a case of disseminated Mycobacterium avium—intracellulare (MAI). Since then it has become in increasingly clear that opportunistic infection by mycobacteria in AIDS is a major complication of the syndrome, with serious implications for the public health of many societies, especially in Africa. The synchrony of both mycobacterial and human immunodeficiency virus (HIV) infection results in clinical presentations, complications and outcomes that are often very different from the same mycobacterial infections in those without HIV infection. There is already considerable clinical experience of combined infections and this review will discuss those reports dealing first with the non-tuberculous mycobacteria and then with tuberculosis. It concludes with a discussion of the mechanisms thought to be underlying the association of mycobacterial infections in AIDS and other immunocompromised states.