Men Who Have Sex With Men (MSM) - Definition

Putting Aside Sexual Identity to Better Track HIV Infection

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Photograph © Mendolus Shank

Men Who Have Sex With Men (MSM) is the term used to categorize males who engage in sexual activity with other males, regardless of how they identify themselves. The term was created in the 1990s by epidemiologists as a surveillance tool to better identify the route of HIV transmission and spread of the disease through male-male sexual activity.

Prior to this, researchers were limited by the identity-based analyses—whereby men who identified as "gay" or "bisexual" weren't necessarily sexually active, while those who identified as "straight" might be sexually active with other men.

The term "MSM" instead focuses on behavior rather than cultural or social self-identification, thereby providing a clearer picture of HIV prevalence (and, in turn, a better understanding of the implications related to HIV prevention).

Studies vary by community and culture, but research conducted by the New York City Department of Health and Mental Hygiene revealed that, of 4,200 men interviewed by telephone:

  • Nearly one in ten who identified as "straight" had sex exclusively with other men.
  • 70% of married men who identified as "straight" engaged in male-male sexual activity at one time or another.
  • 10% of married men who identified as "straight" had reported same-sex behavior during the course of the previous 12 months

HIV Statistics Among MSM in the U.S.

While MSM represent only an estimated two percent of the U.S. population, as a population they account for 55 percent of all HIV infections. According to the Center for Disease Control and Prevention (CDC), if the current trend continues as many as one in six MSM will be infected with HIV in the course of a lifetime.

The prospects appear even more grim for African American MSM, with current projection suggesting an astonishing 50 percent lifetime risk of acquiring HIV.

In their 2014 surveillance, the CDC further noted key disparities in HIV infections among MSM:

  • MSM represented 67 percent of all new HIV diagnoses and 83% of new diagnoses among men 13 and over.
  • Young MSM between the ages of 13 and 24 at greatest risk, accounting for 92% all new infections among men.
  • HIV rates among Hispanics/Latinos are of growing concern. While new HIV diagnoses among white and African American MSM have been relatively steady (down by six percent and two percent, respectively, since 2010), rates among Hispanic/Latino MSM have increased by 13 percent.
  • Today, there is an estimated 687,000 HIV-positive MSM in the U.S. Of these, 15 percent remain undiagnosed.
  • Among those diagnosed with HiV, only 57 percent remain linked to HIV-specific care for more than a year following diagnosis, while only 58% on HIV therapy were able to sustain undetectable viral loads indicative of treatment success.

These statistics align, to some degree, with HIV epidemics in other parts of the world. While the incidence of HIV (the number of infections occurring over a specific period) may be higher in some countries, the HIV prevalence (the portion of a population affected) is almost universally higher among MSM.

Epidemiological research has suggests that the HIV prevalence among MSM is between three and six times greater in the Middle East, Europe, East and Central Asia, and the Oceanic region, and anywhere from 15 to 25 times greater in sub-Saharan Africa, Central America, South America, and South and Southeast Asia.


Pathela, P.; Hajat, A.; Schillinger, J.; et al. "Discordance between Sexual Behavior and Self-Reported Sexual Identity: A Population-Based Survey of New York City Men." Annals of Internal Medicine. September 19, 2009; 145(6):416-425.

Centers for Disease Control and Prevention (CDC). "HIV Among Gay and Bisexual Men." Atlanta, Georgia. Accessed September 22, 2016.

CDC. "Lifetime Risk of HIV Diagnosis in the United States." Atlanta, Georgia; published February 23, 2016.

Beyrer, C.; Baral, S.; van Griensven, F.; et al. "Global epidemiology of HIV infection in men who have sex with men." Lancet. July 28, 2012; 380(9839):367-377.

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