What are HIV and AIDS?
HIV attacks and destroys cells of the body's immune system. This damage progressively weakens the body's ability to fight infections and certain cancers.
The most advanced stage of HIV infection is known as AIDS.
People with AIDS are at great risk of getting very sick from conditions that are more common and more severe in people with weakened immune systems. These conditions include viral infections that cause skin tumors and pneumonia; fungal infections of the mouth, lungs, and genitals; and certain cancers.
AIDS was first reported in the United States in 1981; it is now recognized that HIV is a major worldwide epidemic.
Today, most people with HIV do not develop AIDS thanks to highly effective treatments that stop progression of HIV and allow people with HIV to live long, healthy lives. For this reason, this information focuses mostly on HIV instead of AIDS.
HIV.gov has a more comprehensive description of HIV and AIDS.