The global response to the HIV/AIDS epidemic has improved access to antiretroviral therapy (ART) and has contributed to decreased HIV/AIDS morbidity and mortality in sub-Saharan Africa. Patient adherence to ART is crucial to the success of HIV/AIDS treatment. However, little is known about the determinants of adherence to ART among people living with HIV/AIDS (PLWHA) in the Democratic Republic of Congo (DRC). This qualitative study used in-depth semi-structured patient interviews, a purposive sampling strategy and thematic analysis scheme to identify barriers and facilitators of adherence to ART in the DRC. We recruited three categories of participants from the Centre Hospitalier Monkole and the NGO ACS/Amo-Congo including participants on antiretroviral (ARV) treatment (n = 19), on ARV re-treatment (n = 13) and lost to follow-up (n = 6). Among 38 participants interviewed, 24 were female and the median age was 41 years. Food insecurity as a barrier to adherence emerged as a dominant theme across the three categories of participants. Other barriers included financial constraints, forgetfulness and fear of disclosure/stigma. Religious beliefs were both a barrier and a facilitator to ART adherence. We found that food insecurity was a common and an important barrier to ART adherence among patients in the DRC. Our findings suggest that food insecurity should be appropriately addressed and incorporated into ARV treatment programs to ensure patient adherence and ultimately the long-term success of HIV treatment in the region.