The social identity theory postulates that membership in homogeneous groups could result in a strong identity derived from these groups. Under certain conditions this could result in ingroup bias where group members favour their own group over outgroups. Similar phenomena have been reported in the social capital literature, where dense bonding groups display high levels of intragroup trust, but less trust in other groups in the society. The present study applied the social identity theory as a framework for understanding the association between intragroup trust and trust in other networks. The participants of the study were 200 HIV positive men and women engaging in a support group in KwaZulu-Natal, South Africa. The study included three questionnaires, the first assessing motivation for joining a group, the second assessing social identity derived from the group (collective self-esteem scale) and the third examining the notion of trust against bonding, bridging and linking networks. The results were mixed: Social identity was both negatively and positively associated with general trust, and mostly positively associated with trust in linking networks. The findings imply that social identity theory and ingroup bias could be a fruitful explanation for the negative association between intragroup trust and general trust. Limitations of the study are discussed.