Background and Purpose: People with chronic illnesses, such as Human Immunodeficiency Virus (HIV) infection, face many barriers in the way of adherence to the treatment. In this study, the researchers attempted to investigate the barriers and facilitators of adherence to Antiretroviral Therapy (ART) among patients with HIV. Materials and Methods: Focus group discussion (FGD) was conducted with the primary objectives of investigating the barriers to ART adherence. Nine participants with HIV infection were recruited through a purposive sampling method at Great Tehran Prison. Results: In terms of the influencing factors of non-adherence; the drug side effects, especially with Efavirenz, Methadone and opioids effects resolution due to interaction with antiretroviral drugs, forgetfulness, fear of hangover due to the missed or delayed Methadone use, inappropriate nutrition and lack of access to food supplements and poverty were noted by the majority of participants. In addition, there were some less, but still important factors of non-adherence among the patients, which were mentioned in the manuscript of the article. Conclusion: The medications side effects, inappropriate methadone prescription, stigma, lack of family support, and unfavorable prison conditions were found to be the potential barriers of adherence to HIV medication, whilst a strong and realistic patient-physician relationship, psychosocial and family support, and knowledge regarding the level of CD4 were amongst the possible facilitators for adherence to HIV medication in HIV-positive prisoners.