Two main elements confirm the interest of a prevalence survey of NTM infections in cystic fibrosis (CF) patients: the diagnostic difficulty of "true" infections (as opposed to simple colonizations) to NTM, and the clinical impact on respiratory functions of NTM present in these patients. Two recent contradictory studies on the impact of NTM infections in CF patients have recently been published (Qvist et al., 2015; Albrecht et al., 2016). The German monocentric study suggests a greater deterioration of respiratory function in CF patients not infected with NTM compared to CF patients infected with NTM. 26 patients were infected with NTM: 14/26 with M. avium complex (MAC), 10/26 with M. abscessus complex and 2/26 with M. gordonae. Only 5 patients out of a dozen positive to M. abscessus and 1 in 14 positive to MAC were treated. Comparatively, Qvist et al. found a significant deterioration in respiratory function (maximum expired volume in 1 seconde) of CF patients infected with M. abscessus. This Scandinavian national study reinforced its argument by the fact that an effective treatment made it possible to find changes in maximum expired volume in 1 seconde close to that observed before the infection. Some differences are observed in these two studies; including the age of the subjects included, older in the German study, and the number of positive lung samples per patient. The German study retained the criteria of the American Thoracic Society (ATS) / Infectious Disease Society of America (IDSA) for interpreting respiratory specimens positive for MNT (Griffith et al., 2007). However, these criteria remain very difficult to apply for CF patients because the clinical and radiological manifestations of cystic fibrosis and mycobacterial infection are confounded and other criteria are necessary, such as the number of positive pulmonary samples: 5 vs. 2 to 4 (Qvist et al., 2015) or the decline in maximum expired volume in 1 seconde in the year prior to colonization / MNT infection (-5.8% per year vs. 0.7% per year) (Martiano et al. , 2014). We see here the necessity of complementary studies, in order to be able to identify the diagnostic difficulties and the impacts of the therapeutics administered in these patients. Indeed, on the one hand the therapeutic impact is very difficult to evaluate in the face of the very weak correlation between the results of the "antibiograms" and therefore in vitro and the therapeutic effect in vivo. On the other hand, precise diagnostic interpretation remains essential, as published observational studies show real discrepancies, largely due to diagnostic biases. Recently, under the auspices of the American Foundation and the European Cystic Fibrosis Society, guidelines for the management of NTM infections in CF patients have been published (Floto et al., 2016). To this is added the references of Microbiology (Anonymous, 2015).