Because of their often profound immune suppression, persons with HIV-infection are, increasingly, being identified as having morbidity related to mycobacteria. Indeed, mycobacterial disease is now the second most frequent cause of illness in AIDS patients receiving PCP prophylaxis with the majority of these patients in the United States having disease caused by M. avium complex (MAC). This section reviews the epidemiology, clinical presentation, treatment protocols, and prophylaxis strategies for MAC, as well as the other species of nontuberculosis mycobacteria being diagnosed in the setting of HIV infection. These organisms typically cause extrapulmonary, often disseminated disease in HIV infected persons, although pulmonary disease may occur. The prompt diagnosis and successful treatment of these infections can prolong the life and enhance its quality for affected patients with HIV coinfections.