We report prosthetic knee arthritis in a 55-year-old diabetic man due to Granulicatella adiacens, a micro-organism present in the oral flora, usually described in endocarditis but rarely in prosthesis joint infection. This patient had undergone a dental extraction without antibiotic prophylaxis one month before, and an aseptic loosening of the prosthesis had been diagnosed previously. If antimicrobial prophylaxis against infective endocarditis for dental procedures is well established, such an approach is still controversial for joint prosthesis and should be considered in some conditions.