In all of Asia, an estimated 5.0 million people were living with HIV in 2007. Although overall adult HIV prevalence in South and South-East Asia is still relatively low at 0.3%, the HIV epidemic affects a large number of people - an estimated 4.0 million were living with HIV in this subregion in 2007.

The epidemics in Cambodia, Myanmar and Thailand all show declines in HIV prevalence, with national HIV prevalence in Cambodia falling from 2% in 1998 to an estimated 0.9% in 2006. However, epidemics in Indonesia (especially in its Papua province), Pakistan, and Viet Nam are growing rapidly. Currently in Asia, only China, India and Thailand have more people living with HIV than Viet Nam. In Viet Nam, the estimated number of people living with HIV more than doubled between 2000 and 2005. New HIV infections are also increasing steadily, although at a much slower pace, in Bangladesh.

In India, HIV estimates were lowered in 2007 due to improved surveillance and methods of analysis, but the absolute numbers are still great and the epidemic varies greatly across different regions. In the four southern states (Andhra Pradesh, Karnataka, Maharashtra and Tamil Nadu) where the large majority of people living with HIV in India are believed to reside, HIV prevalence varies, and the epidemic tends to be concentrated in certain districts and associated with unprotected sex between sex workers and their clients.

Injection drug use is a major cause of HIV infection in Southeast Asia, though there are diverse modes of transmission. There is also a relationship between injection drug use and unprotected paid sex. In a 2005-2006 survey in Viet Nam, between 20% and 40% of injecting drug users (depending on the area surveyed) said that they had bought sex in the previous 12 months, and up to 60% said that they regularly had sex. In Indonesia, Although the epidemic was initially powered by HIV transmission among injection drug users, about 15 years later, injection drug users no longer comprise the majority of people infected with HIV.