The human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS), is a virus. Over time, a person with untreated HIV is likely to develop AIDS and fall victim to multiple, concurrent illnesses and possible death. HIV can be transmitted by contact with the blood or other body fluids of an infected person. Among drug users, HIV transmission can occur through sharing needles and other injection paraphernalia. HIV/AIDS has become one of the deadliest pandemics in human history. Populations that are at increased risk for HIV/AIDS include: African-Americans and African-American women, Hispanics, and homosexual men who remain the largest transmission category. Early detection can help in the prevention of HIV transmission, which includes HIV screening. For drug abusing populations, cumulative research has shown that comprehensive HIV prevention is the most effective way to reduce the risk of blood-borne infections. Since the mid-1990s, HIV/AIDS has been treatable through the use of highly active antiretroviral therapy (HAART). In addition, behavioral treatments for drug abuse have shown promise. In addition to increasing their risk of HIV infection, drug use puts individuals at risk for contracting or transmitting hepatitis C (HCV), hepatitis B (HBV), tuberculosis (TB), as well as a number of sexually transmitted diseases, such as syphilis, gonorrhea, and genital herpes. This fact sheet provides the who, what, and how of drug abuse and the link to HIV/AIDS and other infectious diseases.