What's the difference between HIV and AIDS?

- AIDS really just means a more advanced stage of HIV.
Healthy, HIV negative adults have a cd4 count of between 500 and 1,500.
When a person with an HIV-weakened immune system has a cd4 (or T cell) count below 200, or if that person comes down with one or more rare 'opportunistic infections', he may be diagnosed by a doctor as having AIDS.
- "AIDS" stands for "Acquired Immune Deficiency Syndrome." The "syndrome" part means that AIDS is not a single disease but a collection of diseases.
Proper treatment, however, can prevent HIV from turning into AIDS and can restore the health of people with AIDS.
Of the over 1 million people living in the U.S. today with HIV, most do not have AIDS.1
1U.S. Department of Health & Human Services

"AIDS is the most advanced stage of infection caused by HIV. Most people who are HIV positive do not have AIDS.
An HIV-positive person is said to have AIDS when his or her immune system becomes so weak it can't fight off certain kinds of infections and cancers."
- US Office of Public Health