Our objective was to characterise the CT features of the various species of non-tuberculous mycobacteria (NTM) and to identify differences, if any, between Mycobacterium avium intracellulare( MAI) and other species. Fifty-five patients, who were culture positive on at least two occasions for a single NTM species, were evaluated. All patients had CT scans performed within 6 months of NTM identification. The CT scans were assessed for the presence and severity of bronchiectasis, nodules, cavities, tree-in-bud pattern, consolidation and for evidence of pre-existing lung disease. Bronchiectasis was identified in most patients (52 of 55, 95%) and nodules were present in approximately half (29 of 55, 53%). Patients with MAI ( n=16) were found to have significantly higher bronchiectasis scores and higher prevalence of nodules than the other species (both p<0.01). Patients with M.kansasii ( n=9) and M.xenopi ( n=9) had cavities, tree-in-bud pattern, and pre-existing emphysema as the dominant CT features. Patients with M.chelonae and M.fortuitum were younger than the other groups and also had a high incidence of pre-existing lung disease. Patients with MAI infection have more severe bronchiectasis and more nodules on CT than the other NTM species. Morphological differences between the other species were identified but were less distinct.