During the last three decades, both the injection of illicit psychoactive drugs and HIV infection among injecting drug users (IDUs) have spread throughout industrialized and developing countries. Extremely rapid transmission of HIV has occurred in IDU populations with incidence rates of 10 to 50/100 person-years. In sharp contrast, there are many examples of very effective HIV risk reduction for IDUs, both in preventing initial epidemics and in bringing existing epidemics under control. IDUs are capable of learning basic information about HIV/AIDS and modifying their behavior to protect both themselves and their peers. Effective HIV prevention for IDUs requires programs that treat IDUs with dignity and respect, provide accurate information and the means for behavior change-access to sterile injection equipment, condoms, and drug abuse treatment. Programs that provide these services need to be implemented on a public health scale for IDU populations at risk for HIV infection.