Mycobacterium chimaera arouses an increasing public health concern, as this non-tuberculous mycobacterium (NTM) has recently been associated with life-threatening cardiac infections. M. chimaera and Mycobacteriumintracellulare are genetically very close but recently appeared to present different epidemiological and clinical significance. Therefore, it has become important for laboratories to use adequate techniques allowing precise species identification. To date, most commercially available laboratory assays cannot distinguish them and erroneously identify M. chimaera as M. intracellulare. We performed a re-analysis of the 149 M. intracellulare strains received by the Belgian National Reference Laboratory using 16S rRNA gene sequencing, representing 25 % of all NTM collected in 2015. We found that M. chimaera represents the majority (n=94, 63 %) of the previous M. intracellulare. This study reports the large presence of M. intracellulare/chimaera among Belgian patients infected by an NTM and the predominance of the species M. chimaera among this group. This study also stresses the public health importance of M. chimaera and demonstrates the inability of commonly used laboratory techniques to correctly diagnose these infections.