To identify potential risk factors, the CDC (Centers for Disease Control and Prevention), in collaboration with French and British health authorities, conducted a retrospective case-control study using reports submitted to the national surveillance systems of the United States, France, and the United Kingdom. This report describes the study and summarizes its findings, which suggest that certain characteristics of the accidental exposure and the source patient are among the risk factors for HIV transmission. Additionally, the use of AZT prophylaxis by healthcare workers was found to be associated with a lower risk of HIV transmission.