Health care workers are exposed to a wide range of occupational hazards that often depend on the nature of their work. The term health care worker may include workers directly involved in the delivery of patient care, such as physicians, dentists, podiatrists, chiropractors, nurses, nursing assistants, physicians assistants, and therapists. The term may also include workers in health care facilities who do not provide patient care but provide services integral to the function of the facility. These include laboratory workers, maintenance and custodial staff, security personnel, and administrative staff working in a variety of settings including hospitals, outpatient clinics, private practitioner's offices, long-term care facilities, and home health care. Table 1 lists some of the hazards in health care and the work with which they are associated. This article provides an overview of data from existing surveillance systems of health care worker illness and injury, including systems operated by the Centers for Disease Control and Prevention (CDC) (e.g., human immunodeficiency virus [HIV], hepatitis, tuberculosis surveillance) and US Department of Labor, Bureau of Labor Statistics (Survey of Occupational Injuries and Illnesses, and the Census of Fatal Occupational Injuries). Although health care workers confront a variety of occupational hazards, surveillance of the resultant illnesses and injuries often is limited or incomplete. Whenever possible, this article presents descriptive epidemiology data regarding particular hazards. Other articles in this issue explore in greater detail the epidemiology of specific illnesses and injuries and the risk factors associated with them.