Homophily promotes the development of social relationships within social groups and increases segregation across groups. Although prior research has demonstrated that network segregation operates in many dimensions such as race and gender, sexual orientation has received little attention. This study investigates what accounts for the segregation between gay, lesbian and bisexual friends and straight friends in GLB youth’s personal networks by testing three possible underlying mechanisms – structural constraints, choice homophily and compartmentalization attempts. The analysis uses data collected from GLB youth who were becoming members of a community organization in Indiana from 1994 through 1998. Although the small, convenience sample does not allow generalization of the results, the rich network data provide important insights into personal network segregation in this unique social context. The results suggest that the segregation between GLB and straight friends result from structural constraints and friends’ preference to interact within their groups, and that the focal GLB youth’s effort to compartmentalize his or her sexual identity accounts little for the segregation.