The prevalence of the nontuberculous mycobacteria (NTM) among clinical mycobacterial isolates is increasing. Reports of human pulmonary disease ascribed to these isolates, particularly the Mycobacterium avium complex, have involved hosts who did not possess the traditional risk factors of structural airways disease or apparent conditions that alter local or systemic immune function. More definitive evidence supporting a causal relationship between recovery of M. avium complex and the presence of small peripheral nodules with or without focal bronchiectasis now exists from biopsy studies as well as longitudinal evaluations. The concept of airway colonization, the nonpathogenic presence of NTM in the lower airways, is less viable. However, given the very slowly progressive nature of noncavitary disease, the remaining question is whether to aggressively treat patients with a multidrug regimen or to diligently follow them with frequent microbiologic and radiologic evaluations. The advent of the newer macrolide-azide antibiotics with demonstrated effectiveness against M. avium complex has significantly improved the management outcome of multidrug chemotherapeutic regimens. The potential for prevention of significant bronchiectatic lung disease merits an aggressive diagnostic approach to identify NTM in the appropriate clinical presentation. Recognizing the changing presentations of NTM pulmonary disease is requisite for suspecting NTM as potential etiologic agents.