HIV-positive injection drug users (IDUs) are at risk for transmitting HIV to their sex and injection partners, and compared with non-IDUs, they have poorer access to medical care and adherence to antiretroviral therapies. Social support has been linked with decreased injection and sexual risk behaviors and slower disease progression. In this qualitative process evaluation, we explored emotional support (ie, caring, empathy), informational support (ie, information, guidance, feedback), and appraisal support (ie, information for self-evaluation or understanding) received by participants in the Interventions for Seropositive Injectors-Research and Evaluation (INSPIRE) project, a multisite secondary prevention intervention for HIV-positive IDUs. Participants in the intervention and control conditions (N=40) described similar experiences in terms of type, source, and perceived benefits of social support received from the program. Emotional support was received from program staff, other participants, and elements of the intervention. Participants also mentioned social support received from the INSPIRE project in relation to changes they had made in their lives during and after their involvement in the intervention, such as changes in their drug use, sexual practices, and health care utilization.