Men who have sex with men are at the core of the HIV epidemic in every country in the world. But social and governmental denial, stigma, and violence against those who transgress sexual norms have helped to hide this fact and impede efforts to prevent new HIV infections.

At one extreme are Iraq and Iran, where religious fundamentalists have hunted down and killed hundreds of people whom they believe to be gay. Further along the spectrum are scores of nations where draconian sodomy laws are aggressively enforced, with penalties that include years in prison. Political and religious leaders in Botswana even tried to quash research into the subject, claiming that same sex activity did not exist in that country.

“General population heterosexual transmission is the major source in only two regions, Africa and the Caribbean,” says David Wilson, lead health specialist of the global HIV/AIDS programme at the World Bank. But even in these regions, men who have sex with men are about four times more likely than heterosexuals to be infected with the virus, according to the scant data that are available.

A literature review published last year found that globally, men who have sex with men are 19 times more likely to be infected with HIV …