The burden of HIV/AIDS in China is due to injection drug use. Non-clinical caregivers provide much of the care for HIV patients but are often not included in HIV care or research. The objective of this study is to examine the relationships between the caregiver context and mental health of HIV-positive injection drug users and their caregivers. We interviewed 96 patient-caregiver dyads using quantitative methods. A conceptual model was developed as a framework for multivariate linear regression modeling. The strongest predictor of poor patient mental health was lack of social support, which was largely determined by the caregiver's stigma towards HIV/AIDS and caregiver burden. Patient disability and caregiver burden were the primary predictors of poor caregiver mental health. The interrelated nature of caregiver and patient mental health supports the inclusion of caregiver health into the patient's HIV/AIDS treatment to maximize support provision and health for the patient and caregiver.