Phil Johnson, M.D. discusses the evolution of the definition of AIDS over time and how it evolved as scientific understanding of HIV and AIDS improved over time. Initially it was noticed due to unusual outbreaks of Kaposi's Sarcoma and pneumocystis pneumonia among young gay men and referred to as Gay Related Immune Deficiency. The virus now referred to as HIV was isolated in 1983 and the disease was renamed AIDS for Acquired Immune Deficiency Syndrome. Today, being HIV positive and having either (a) a CD4 cell count below 200 or (b) one of a number of opportunistic infections results in a diagnosis of AIDS.