'Mycobacterium sherrisii' is an undescribed species that appears to be emerging, in particular, among HIV-positive patients originating from Africa. To describe 'M. sherrisii', to ensure that the species name is validly published and to define its phylogenetic position, we collected 11 of these strains reported in five previous studies, and subjected them to biochemical identification, cell-wall mycolic acid analysis and sequencing of multiple housekeeping genes. The bacteria formed smooth and generally non-chromogenic colonies after 2-3 weeks of subculture at 24-37 °C; photochromogenic and scotochromogenic pigmentation were exhibited by three and two strains, respectively. The strains were positive for the heat-stable catalase test, but negative in tests for hydrolysis of Tween 80, nitrate reduction, β-glucosidase and 3-day arylsulfatase. Mycolic acid patterns, obtained by HPLC, resembled a trimodal profile similar to those of type strains of Mycobacterium simiae, Mycobacterium lentiflavum, Mycobacterium triplex and Mycobacterium genavense. The 16S rRNA gene sequences of the 11 strains differed by 4 bp (99.7 % similarity) from that of the type strain of the closest related species, M. simiae ATCC 25275(T). Levels of internal transcribed spacer (ITS) and partial hsp65 and rpoB gene sequence similarity between the two taxa were 95.8 % (271/283 bp), 97.5 % (391/401 bp) and 95.2 % (700/735 bp), respectively. On the basis of these results, we propose the formal recognition of Mycobacterium sherrisii sp. nov. The type strain is 4773(T) ( = ATCC BAA-832(T) = DSM 45441(T)).