A new case of late bacterial endocarditis caused by Cardiobacterium hominis is reported. The infection developed on an aortic valve prosthesis and responded favourably to medical treatment. The main characteristics of the micro-organism and of the oslerian graft are reviewed in the light of published data. The problem of endocarditis with negative blood cultures is discussed since C. hominis is reputed difficult to cultivate, although this was not the case in our patient.