The average estimated risk of human immunodeficiency virus (HIV) infection for health care workers following a percutaneous or mucous exposure is <0.5% in incidence studies, although a case-control study suggests it is much higher for highest-risk percutaneous exposure. To characterize exposures resulting in HIV transmission, we reviewed available data on occupational cases reported worldwide, identifying 94 documented and 170 possible cases. The majority of documented infections occurred in nurses, after contact with the blood of a patient with AIDS by means of percutaneous exposure, with a device placed in an artery or vein. High-exposure job categories, e.g., midwives and surgeons, are represented mostly among possible cases. Transmission occurred also through splashes, cuts, and skin contaminations, and in some cases despite postexposure prophylaxis with zidovudine. Health care workers could benefit if these data were incorporated in educational programs designed to prevent occupational bloodborne infections.