Men who have sex with men (MSM) in the USA were the first population to be identified with AIDS and continue to be at very high risk of HIV acquisition. We did a systematic literature search to identify the factors that explain the reasons for the ongoing epidemic in this population, using a social-ecological perspective. Common features of the HIV epidemic in American MSM include role versatility and biological, individual, and social and structural factors. The high-prevalence networks of some racial and ethnic minority men are further concentrated because of assortative mixing, adverse life experiences (including high rates of incarceration), and avoidant behaviour because of negative interactions with the health-care system. Young MSM have additional risks for HIV because their impulse control is less developed and they are less familiar with serostatus and other risk mitigation discussions. They might benefit from prevention efforts that use digital technologies, which they often use to meet partners and obtain health-related information. Older MSM remain at risk of HIV and are the largest population of US residents with chronic HIV, requiring culturally responsive programmes that address longer-term comorbidities. Transgender MSM are an understudied population, but emerging data suggest that some are at great risk of HIV and require specifically tailored information on HIV prevention. In the current era of pre-exposure prophylaxis and the undetectable equals untransmittable campaign, training of health-care providers to create culturally competent programmes for all MSM is crucial, since the use of antiretrovirals is foundational to optimising HIV care and prevention. Effective control of the HIV epidemic among all American MSM will require scaling up programmes that address their common vulnerabilities, but are sufficiently nuanced to address the specific sociocultural, structural, and behavioural issues of diverse subgroups.