The AIDS epidemic is having an increasing impact on the practice of emergency medicine. In inner-city emergency departments, significant numbers of patients have unrecognized human immunodeficiency virus (HIV) infection. Transmission of HIV in the health care setting has been predominantly from exposure to patients' infected blood, but most of the exposures (80%) are due to injuries from sharp instruments. There are only 18 documented cases of occupational HIV transmission worldwide. Four of these have occurred from nonparenteral exposures. Based on surveillance studies, the best estimate of seroconversion after exposure is about 0.5%. However, due to methodologic limitations, these figures may be underestimations. The effectiveness of azidothymidine for postexposure prophylaxis has not been shown. Currently, the best protection against HIV and other blood-borne pathogens remains use of universal precautions.