Social capital, defined as the sum of an individual’s resource-containing, reciprocal and trustworthy social network connections, has been associated with improved engagement in care among people living with HIV globally. We conducted a qualitative interview study of social capital among 28 young Black gay, bisexual and other men who have sex with men ages 18–29 living with HIV in Atlanta, Georgia. We asked participants about bonding capital (relationships between individuals with similar demographic characteristics), bridging capital (relationships with individuals of different backgrounds), collective efficacy (involvement with community organisations) and satisfaction with their social networks. We found that participants described bonding capital from friends and family in depth, while more gaps were noted in bridging capital and collective efficacy. Bonding capital derived from families was especially critical to participants’ satisfaction with their social capital. Findings suggest that interventions targeting young Black gay, bisexual and other men who have sex with men should build upon strong bonds with family and friends, and/or fill gaps in bridging capital and collective efficacy by connecting young men to mentors and organisations.