We report two cases of endocarditis due to Moraxella osloensis. Only one previous case of such infection has been described. These infections occurred in immunocompromised patients (B-cell chronic lymphocytic leukaemia and kidney graft associated with Hodgkin's disease) and both patients had a favourable outcome with a complete cure of their infectious endocarditis. This bacterium could be an emerging pathogen revealed by MALDI-TOF. Indeed, its characterisation within the Moraxella group by use of biochemistry-based methods is difficult. Moreover, this strain could be particularly involved in immunocompromised patients.