Housing is a known determinant of health behaviors, which includes adherence to Antiretroviral Therapy (ART). Within the Longitudinal Investigations into Supportive and Ancillary Health Services (LISA) study, unstable housing is inversely associated with adherence. Several comprehensive adherence support services have emerged to improve adherence for unstably housed or otherwise vulnerable populations. The Maximally Assisted Therapy (MAT) program in Vancouver, British Columbia uses a multidisciplinary approach to support HIV-positive clients with a history of addictions or mental illness, many of whom also experience episodic homelessness. This study investigated the association between antiretroviral adherence and use of support services, including the MAT program, amongst people living with HIV and AIDS who are unstably housed in the LISA sample. Of the 212 unstably housed participants, those who attended the MAT program were 4.76 times more likely to be ≥95% adherent (95% CI 1.72-13.13; P = 0.003) than those who did not. The findings suggest that in the absence of sustainable housing solutions, programs such as MAT play an important role in supporting treatment adherence in this population.