A new, slow-growing, scotochromogenic mycobacterium was isolated from a lymph node of an immunocompromised child and subsequently from tap water and from a respiratory specimen of a patient with chronic fibrosis. Alcohol-acid-fastness, lipid patterns and the G+C content clearly support the placement of this organism in the genus Mycobacterium. The isolates grew very slowly at temperatures ranging from 25 to 32 °C and showed activities of nitrate reductase, catalase, urease, arylsulfatase and Tween 80 hydrolysis. The organism was susceptible to all antimycobacterial drugs tested. The 16S rDNA sequence was unique and phylogenetic analysis placed the organism close to fast-growing species such as Mycobacterium farcinogenes, Mycobacterium komossense and Mycobacterium aichiense. These data support the conclusion that the isolates represent a new mycobacterial species, for which the name Mycobacterium tusciae sp. nov. is proposed. The type strain is strain Fl-25796T; a culture of this strain has been deposited in the DSMZ as strain DSM 44338T.