Recent international guidelines published in 1997 and 1999 have proposed diagnostic and treatment criteria for disease caused by nontuberculous mycobacteria (NTM). In this paper, the epidemiological data, diagnostic criteria, treatment regimens and outcomes from 117 HIV-negative patients who had a positive culture for NTM between 1995-1999 are reviewed. The authors wished to identify factors associated with improved outcome in these patients. A total of 71 patients were believed to have a clinical disease caused by NTM, as defined by international criteria. A total of 72% patients were found to have had pulmonary disease. There was a rise in infections between 1995-1999, with a peak in infections in 1997. The most striking rise was in Mycobacterium avium intracellulare complex infections (1995: 33% infections; 1996: 36% infections; 1997: 41% infections; 1998: 61% infections; 1999: 57% infections). There was a link between deprivation and number of positive NTM isolates (34.4% isolates occurred in the areas of lowest Carstairs deprivation index versus 20.6% isolates from areas of least deprivation). There was a significant association between appropriate therapy, defined by American Thoracic Society and British Thoracic Society guidelines, and successful outcome (74%) in contrast to those who received inappropriate treatment prior to the publication of these guidelines. Nontuberculous mycobacteria infections remain a significant problem in non-HIV patients. Adherence to published guidelines may improve patient outcomes.