BACKGROUND: Non-tuberculous mycobacteria have long been identified as capable of causing human disease and the number at risk, due to immune-suppression, is rising. Several reports have suggested incidence to be increasing, yet routine surveillance-based evidence is lacking. We investigated recent trends in, and the epidemiology of, non-tuberculous mycobacterial infections in England, Wales and Northern Ireland, 1995-2006. METHODS: Hospital laboratories voluntarily report non-tuberculous mycobacterial infections to the Health Protection Agency Centre for Infections. Details reported include age and sex of the patient, species, specimen type and source laboratory. All reports were analysed. RESULTS: The rate of non-tuberculous mycobacteria reports rose from 0.9 per 100,000 population in 1995 to 2.9 per 100,000 in 2006 (1608 reports). Increases were mainly in pulmonary specimens and people aged 60+ years. The most commonly reported species was Mycobacterium avium-intracellulare (43%); M. malmoense and M. kansasii were also commonly reported. M. gordonae showed the biggest increase over the study period rising from one report in 1995 to 153 in 2006. Clinical information was rarely reported. CONCLUSIONS: The number and rate of reports increased considerably between 1995 and 2006, primarily in older age groups and pulmonary specimens. Increases in some species are likely to be artefacts but real changes in more pathogenic species, some of which will require clinical care, should not be excluded. Enhanced surveillance is needed to understand the true epidemiology of these infections and their impact on human health.