AIDS first recognized in 1981. AIDS indicates presence of an underlying cellular immune deficiency in a patient with no known underlying cause other than HIV infection. (a) Homosexuals, (b) IV drug addicts, (c) Blood transfusion recipients, and (iv) Heterosexual partners. Immunology: (a) Decrease number of helper T-lymphocytes, (b) Absolute lymphopenia, and (c) Impaired response on skin testing. Virus: (i) 1983: lymphadenopathy associated virus (LAV). (ii) 1984: Human T-cell-lymphotropic virus Type III, now the virus is termed as human immunodeficiency virus (HIV). Diagnosis: (a) ELISA test—screening test and (b) Western blot test— confirmatory for HIV antibodies. Principle of treatment (as available today): Today nucleoside analogue (Zidovudine 200 mg TID and Lamivudine 150 mg BID) with one NNRTI (Non-nucleoside reverse transcriptase inhibitors), e.g. Nevirapine 200 mg TID or Delavirdine 400 mg TID give maximum therapeutic effect.