This chapter discusses clinical manifestations with special reference to ENT for AIDS or HIV, where acquired immunodeficiency syndrome (AIDS) was caused by a microorganism being transmitted through blood and sex. A virus was isolated from an AIDS patient which was named human immunodeficiency virus (HIV) by WHO. HIV, the virus which causes AIDS is a lentivirus, one of the subfamilies of retrovirus, and there are two types of HIV, which are HIV I and HIV II. Persons harbouring HIV in their body are the reservoirs of infection. Infected blood, semen and vaginal fluids are the prime sources of infection. Intravenous drug users (IDU), men sex with men (MSM), commercial sex workers (CSW), truck drivers, jail inmates, etc. are the high risk groups for HIV. There are three main modes of transmission, such as sexual intercourse, blood-borne infections, and HIV-infected human can transmit HIV to her foetus or infant.