This social stigma has prevented many men and boys from admitting that they are at risk of contracting HIV from sex with other men and has prevented the development of HIV prevention campaigns directed at those men at risk. In many parts of the world men who have sex with men are frequently the target of prejudice and discrimination, even legal sanction.

In yet other cases, sex may take place between men because they are the only sex partners available, as in the case of men in prison or in all-male institutions. Others may be married or in a long-term relationship with a woman and occasionally have sex with men, often without their female partner knowing.

Some men may identify themselves as 'homosexual' or 'gay' (specific terms exist in almost all cultures) and have long-term or occasional sexual relationships with other men. Studies confirm that boys and men across the world report sex with other boys and men, with rates of 10-16% in Peru, 5-13% in Brazil, 10-14% in the US, 15% in Botswana and 6-16% in Thailand.