Because of the growing use of implants, infections in prosthetic devices are probably becoming commoner, even though the risk of infection remains low. Multiple factors appear to be involved in the development of these infections, including foreign body-associated tissue damage, impairment of host defenses, bacterial trapping by fibrin, sequestration of bacteria in implant interstices, and the generation of a biofilm on implant surfaces. Although there is a direct association between the tissue reactivity of implants and their ability to potentiate infection, bacterial slime production and adherence to implant surfaces (generation of the biofilm) appear to play a primary role in the pathogenesis of device infections, contemporary prosthetic devices generally being quite nonreactive with respect to host tissues. While virtually any organism can cause these infections, gram-positive bacteria, especially staphylococci, predominate. Infections due to gram-negative organisms and fungi, however, tend to be more serious, often requiring prompt removal of the implant.