Over the past several years, there has been an increasing appreciation of the burden of pulmonary disease caused by nontuberculous mycobacteria (NTM) in both the general population1-3 and in patients receiving immunosuppressive drugs. Soon after the first tumor necrosis factor-α antagonist was introduced into clinical use, the increased risk of mycobacterial infections, TB especially, in patients receiving these agents was recognized.4 Physicians are by now well sensitized to the importance of screening patients with various rheumatic and other systemic inflammatory conditions for TB prior to initiation of treatment with tumor necrosis factor-α blockers. Nearly every practicing pulmonologist by now is aware of the challenges of treating patients with Mycobacterium avium, Mycobacterium xenopi, Mycobacterium abscessus, Mycobacterium kansasii, Mycobacterium fortuitum, and others. It is well appreciated, through both large epidemiologic studies and individual experience, that in economically developed countries that generally have low incidence rates of TB, the burden of NTM infections far outstrips that of TB. Much less well understood, however, are the particular risk factors for developing infections with NTM, the natural history of these infections, and the best approaches to treatment. In this issue of CHEST (see page 563), Brode and colleagues5 make an important contribution to our understanding of the epidemiology of NTM infections and they point the way to important avenues of future research.