An assessment of the current situation of HIV/AIDS among men who have sex with men (MSM) and transgender (TG) populations and the national responses was undertaken by the WHO Regional Office for South-East Asia. The countries assessed are Bangladesh, India, Indonesia, Maldives, Myanmar, Nepal, Sri Lanka, Thailand and Timor-Leste. Same-sex behaviour is identified in all societies, irrespective of whether same-sex sexuality is openly acknowledged, not talked about, or actively denied. There are an estimated 4–5 million men who have sex with men (MSM) in the South-East Asia Region, while the number of those considered to be transgender (TG) is largely unknown due to limited data. MSM and TG populations in most countries of the Region are highly stigmatized, discriminated against, and often socially excluded. As with other most-at-risk populations such as people who inject drugs and sex workers, MSM and the TG populations in the Region are at high risk for HIV infection. Access to prevention, treatment, care and support services is limited compared with the share of the HIV burden borne by these vulnerable populations. This report highlights the urgent need to ensure that prevention interventions, and treatment, care and support services are put in place for MSM and TG populations.