In the United States (U.S.), the HIV infection rate is disproportionately high among incarcerated individuals. HIV-infected individuals typically receive antiretroviral therapy (ART) to suppress HIV and reduce the threat of transmission. Although HIV-infected individuals are generally ART-adherent while incarcerated, the public health benefits experienced during incarceration are often lost as HIV-infected individuals struggle to maintain optimal adherence post-incarceration. While the importance of maintaining adherence in the post-incarceration period has been acknowledged, research on barriers to ART adherence during this period is limited. To better understand post-release barriers to ART adherence, we conducted in-depth interviews with 20 HIV-infected formerly incarcerated individuals in New York City; we also followed up with 18 (90%) participants after three months to explore whether their adherence challenges changed over time. Viral load testing results from their most recent physician visit were also recorded at each interview. Interviews were transcribed using transcription software and reviewed for accuracy by a researcher. Thematic coding based on discussion guide prompts were then used to identify commonly mentioned barriers to adherence. The results identified four overarching themes that affected study participants' efforts to adhere to their ART regimen: medication burden, forgetfulness, mental health and emotional difficulties, and perceived conflict between substance use and medication adherence. These barriers were the most commonly cited and largely persisted at three-month follow-up. The results suggest that interventions addressing these challenges are essential for promoting ART adherence among HIV-infected formerly incarcerated individuals. Effective interventions may include mobile-based text messaging reminders and those that facilitate patient-provider communication. Additionally, interventions or programs that integrate substance use and mental health treatment into HIV-related care, along with other types of behavioral health support, may also be beneficial for this population. Such interventions should be a routine part of discharge planning and support for incarcerated individuals returning to the community.