Healthcare workers (HCWs) are at risk for occupational acquisition of human immunodeficiency virus (HIV) infection, primarily due to percutaneous exposure to infected blood. As of June 1996, 51 documented cases and 108 possible cases of occupationally acquired HIV infection in HCWs in the United States had been reported to the Centers for Disease Control and Prevention. The frequency of blood exposure among HCWs varies according to occupation, procedures performed, and use of preventive measures. Based on limited data, it has been estimated that approximately 500,000 percutaneous blood exposures may occur annually among hospital-based HCWs in the United States. Of these, approximately 5,000 may involve exposures to blood that is known to be HIV infected. The average risk of HIV transmission after percutaneous exposure to HIV-infected blood is approximately 0.3%; however, the risk is believed to be higher for exposures involving an increased volume of blood and/or high viral load.