There is currently a scarcity of research on the nature of HIV/AIDS stigma within the Thai health context. This is problematic given the negative role of stigma in hindering the provision of patient care and treatment. This study used a mixed-method approach to investigate the interrelationships between the stigma of HIV/AIDS and the stigmas relating to its various modes of disease transmission including injection drug use (IDU). Twenty interviews were conducted with trainees and qualified nurses from a Bangkok college. Participants were presented with vignettes describing a hypothetical person varying in disease diagnoses (AIDS, leukemia, no disease) and co-characteristics (IDU, commercial sex (CS), blood transfusion, no co-characteristic). Using a Q-sort task, participants arranged the vignettes along a bipolar scale according to their willingness to interact with the persons, and were asked to explain their decisions. Univariate and multivariate regression analyses showed that IDU, AIDS, and CS were all individually stigmatizing. Strong interactions were found between the stigmas of HIV/AIDS, IDU, and CS. Interview data also showed clear biases toward patients according to their IDU and CS habits. The findings suggest that addressing these co-stigmas could be vital to the success of efforts aimed at reducing the disease stigma of HIV/AIDS.