Mycobacteria have been known since the nineteenth century to be pathogenic for humans. Thus Koch first described the tubercle bacillus in 1882. Before the turn of the century, atypical variants had also been appreciated that were associated with disease in animals. Over time a greater appreciation of these organisms and their means of spread led to better attempts at control and treatment of these agents. With the introduction into society of the human immune deficiency virus (HIV), however, the natural mechanisms by which the body controls the organisms were significantly impaired in HIV-infected patients and atypical forms of mycobacterial disease became prevalent. These organisms have now become one of the most significant threats to these individuals and on occasion may require some form of surgical intervention.