We compared social network characteristics of African American men who have sex with men only (MSMO) with social network characteristics of African American men who have sex with men and women (MSMW). Study participants were 234 African American men who have sex with men who completed a baseline social network assessment for a pilot behavioral HIV prevention intervention in Baltimore, Maryland, from 2006 through 2009. We surveyed the men to elicit the characteristics of their social networks, and we used logistic regression models to assess differences in network characteristics. MSMO were significantly more likely than were MSMW to be HIV-positive (52% vs 31%). We found no differences between MSMO and MSMW in the size of kin networks or emotional and material support networks. MSMW had denser sexual networks, reported more concurrent and exchange partners, used condoms with more sexual partners, and reported interaction with a larger number of sexual partners at least once a week. Although there were many similarities in the social and sexual network characteristics of MSMO and MSMW, differences did exist. HIV prevention interventions should address the unique needs of African American MSMW.