BACKGROUND: HIV disproportionately affects young Black men who have sex with men (YBMSM) in the United States. eHealth holds potential for supporting linkage and engagement in HIV prevention and care and the delivery of HIV information to YBMSM. OBJECTIVE: This study aims to investigate HIV information acquisition and use among YBMSM who use the internet. METHODS: A web-based self-administered survey and semistructured interviews were conducted. The survey findings informed the development of the interview guide. Descriptive statistics were used to characterize the survey sample, and interview data were analyzed thematically using modified grounded theory methodologies. RESULTS: Among the internet sample (N=83), the average age was 29.2 (SD 3.5) years, 41% (n=34) of participants self-reported living with HIV, 43% (n=36) were HIV-negative, and 15% (n=13) were unsure of their HIV status. Most participants (n=79, 95%) acquired HIV information through the internet while using a mobile phone. Web-based HIV information was intentionally sought from consumer health information websites (n=31, 37%), government health information websites (n=25, 30%), and social media (n=14, 17%). Most men incidentally acquired HIV information via advertisements on social media sites and geospatial dating apps (n=54, 65%), posts on social media sites from their web-based social ties (n=44, 53%), and advertisements while browsing the internet (n=40, 48%). Although the internet is the top source of HIV information, health care providers were the most preferred (n=42, 50%) and trusted (n=80, 96%) source of HIV information. HIV information was used to facilitate the use of HIV prevention and care services. The qualitative sample included YBMSM across a range of ages and at different points of engagement in HIV prevention and care. Qualitative findings included the importance of the internet as a primary source of HIV information. The internet was used because of its ease of accessibility, because of its ability to maintain anonymity while searching for sensitive information, and to mitigate intersecting stigmas in health care settings. Participants used HIV information to assess their risk for HIV and AIDS, support their skill building for HIV prevention, inform patient-doctor communication, and learn about HIV prevention and treatment options. Men expressed concerns about their diminishing access to online spaces for HIV information exchange among YBMSM because of censorship policies on social media sites and the stigmatizing framing and tone of mass media HIV-prevention advertisements encountered while using the internet. CONCLUSIONS: YBMSM in this sample had high utilization of eHealth for HIV information acquisition and use but diminished access to their preferred and most trusted source of HIV information: health care providers. Future eHealth-based HIV interventions culturally tailored for YBMSM should aim to reduce intersectional stigma at the point of care and support patient-provider communication. The findings demonstrate the need for community-informed, culturally tailored HIV messaging and online spaces for informational support exchange among YBMSM.