The definition of AIDS has changed over the years. Currently, an AIDS diagnosis (indicating that the person has reached the late stages of the disease) is given to people with HIV who have counts below 200 CD4+ cells/mm3 (also known as T cells or T4 cells, which are the main target of HIV) or when they become diagnosed with at least one of the following diseases: Pneumocystis Carinii Pneumonia (PCP), Kaposi's Sarcoma (KS), HIV Wasting Syndrome, Non-Hodgkin's lymphoma, Cryptococcosis, extrapulmonary HIV encephalopathy (AIDS dementia), Mycobacterium, Avium Intracellulare (MAC or MAI), Candidiasis of the esophagus, trachea, bronqui, or lungs, Cryptosporidiosis, chronic intestinal Tuberculosis, Herpes Simplex virus infection

Progressive Multiphocal Leukoencephalopathy (PML), Primary lymphoma of the brain, Toxoplasmosis of the brain, Histoplasmosis, Isoporidiasis, chronic intestinal, Coccidioidomycosis, Salmonella septicemia, Bacterial infections, recurrent, <13 years

Lymphoid intersticial pneumonia/pulmonary lymphoid hyperplasia, <13 years, Recurrent bacterial pneumonia (two or more episodes in one year) or Invasive cervical cancer.

(Definitions courtesy of the STOP AIDS Project, San Francisco)