We assessed how egocentric (i.e., self-generated descriptions of a person's social contacts) network structure and composition corresponded with reported instances of condomless receptive and insertive anal intercourse with men who were reportedly HIV-infected or of unknown HIV serostatus in a sample of black men who have sex with men (MSM) in six U.S. cities. Ratings showing a higher percentage of network members who provided social participation and medical support were positively associated with reporting condomless sex. There were also significant positive associations between stimulant use and condomless insertive and receptive anal sex. Future research should examine the social processes that underlie these associations and explore ways that social support can affect HIV prevention efforts for black MSM.