The name 'Mycobacterium alsiense', although reported in 2007, has not been validly published. Polyphasic characterization of three available strains of this species led us to the conclusion that they represent a distinct species within the genus Mycobacterium. The proposed novel species grows slowly and presents pale yellow-pigmented colonies. Differentiation from other mycobacteria is not feasible on the basis of biochemical and cultural features alone while genetic analysis, extended to eight housekeeping genes and one spacer region, reveals its clear distinction from all other mycobacteria. Mycobacterium asiaticum is the most closely related species on the basis of 16S rRNA gene sequences (similarity 99.3 %); the average nucleotide identity between the genomes of the two species is 80.72 %, clearly below the suggested cut-off (95-96 %). The name Mycobacterium alsense sp. nov. is proposed here for the novel species and replaces the name 'M. alsiense', ex Richter et al. 2007, given at the time of isolation of the first strain. The type strain is TB 1906T ( = DSM 45230T = CCUG 56586T).