Mycobacterium malmoense was isolated in four different sputum samples of a 45-year-old alcoholic smoker. The biochemical and culture characteristics of this species are described and compared with a reference strain (ATCC 29571). The isolated strain was sensitive in vitro to rifampicine, ethionamide, kanamycine and erythromycin. Therapy consisted of right-upper-lobe lobectomy and a two-year antimicrobial therapy. There was no sign of relapse at the end of the treatment period.