Mycobacterium heckeshornense was responsible for a severe, recurrent and chronic pulmonary infection in an immunocompetent 65-year-old woman. The pathogen, initially identified as Mycobacterium xenopi and considered as a contaminant, led to a delayed adapted antimicrobial treatment. Although M. heckeshornense is phenotypically closely related to M. xenopi, its pathogenicity is noticeably higher. Accurate molecular diagnosis methods and treatment guidelines are needed to improve the management of patients infected by this uncommon pathogen.