Pre-Exposure Prophylaxis (PrEP) has biological efficacy in reducing risk for HIV acquisition but its clinical effectiveness is strongly influenced by patient adherence, which is in turn influenced by social and behavioral factors. Trials conducted among serodiscordant heterosexual African couples who were engaged in supportive romantic partnerships found PrEP to be highly effective for HIV prevention. In contrast, studies with socially marginalized populations in Latin America without strong interpersonal support networks, such as transgender women (TW), found substantially lower levels of adherence and, as a result, effectiveness. We believe that new, social network-based strategies to promote PrEP adherence, coupled with behavioral interventions to minimize risk compensation, will be critical to controlling the spread of HIV among TW in Latin America.