The protective effects of social support on health have been documented in a variety of groups. For HIV-infected persons released from correctional settings, strong social support may be particularly important for obtaining effective postrelease medical treatment and supportive services. Researchers and program evaluators seeking to improve access and adherence to postrelease HIV medical care in this population need accurate measures for the level and type of social support, but current measures have not been fully validated for incarcerated individuals with HIV infection. We used the Rasch model to test the Medical Outcomes Study (MOS) social support survey. Data for the analysis were collected as part of the EnhanceLink project in the five urban jails where the MOS was administered. Findings indicate that the MOS survey items may not capture the entire variability of person abilities. Respondents showed problems in discriminating among response options, indicating potential systematic bias. In addition, while there was no significant gender difference, overall levels of social support differed by gender. Further research is warranted to develop more effective social support measurement tools that can better guide interventions for persons transitioning from jail and prison to the community.