Medical devices have become an integral part of hospital-based care but also predispose patients to more than 850 000 device-related infections annually. Devices predispose to infection by damaging or invading epithelial and mucosal barriers to infection, by supporting growth of microorganisms and thus serving as reservoirs, by impeding host defense mechanisms, and, when contaminated, by directly infecting patients. Epidemics of device-related infections appear to have increased in frequency since 1965, have been due mainly to gram-negative bacilli, usually have resulted from in-hospital contamination of devices, and most often have been linked to urinary catheters, intravenous infusion devices, hemodialysis, and respiratory therapy equipment. Endemic device-related infections include those traced to these same commonly used medical devices as well as infections that follow use of specialized devices such as prostheses. Urinary catheters and intravenous infusion devices represent major sources of nosocomial septicemia. In most instances, measures currently recommended to control device-related infections have not been assessed with respect to either efficacy or practicality, and further study of the pathogenesis and prevention of these infections is needed.