AIDS Education and Prevention 22(6): 483-495 Past studies have primarily focused on individual-level factors influencing the HIV risk practices of gay or bisexual men. The role of one’s social network has been less explored. This study identified 75 indexes in venues frequented by men who have sex with men and then recruited all willing persons named as members of each index’s egocentric social network. Two hundred fifty-five unique network members completed assessments of risk-related characteristics and also sociometric measures that were used to identify the influence leader of each network. White and African American networks were composed primarily of men of the same race. Over 70% of men reported recent casual sexual partners. About one fourth of men engaged in unprotected anal intercourse (UAI) with a casual partner or with multiple partners in the past 3 months. The social network to which a man belonged, weaker risk reduction intentions, and greater substance use independently predicted a range of high-risk sexual behaviors. There were modest but significant correlations between the risk-related characteristics of network members and network leaders. Social network-level approaches are feasible for reaching hidden subgroups of MSM at high risk for contracting HIV.