In the best of all worlds, physicians would base their diagnostic and therapeutic judgments on secure, statistically significant data. Unfortunately, despite nearly a half century of modern scientific medicine, there are many topics that remain obscure. The causes of this confusion are many: the absence of studies, poorly designed studies, or an excessive number of variables that defy analysis in studies of practical scale or expense. Whatever the origins, there are a number of questions in the area of mycobacterial disease for which insufficient data exist to make “definitive” pronouncements. Nonetheless, practitioners are called upon regularly to make public health and clinical judgments in these situations. This document was prepared in full realization of the shortcomings of the data, with the intent of compiling well-informed opinion on these controversial topics. The contributors have rendered their judgments after review of the pertinent available information, knowing that time subsequently may prove them wrong. However, the philosophy underlying the preparation of these “consensus positions” has been that such informed opinion ought to prove useful as working guidelines until definitive data are compiled.