BACKGROUND Adherence to HIV antiretroviral therapy (ART) is of great importance for reducing viral load and the eventual treatment of the patients and minimizing infectivity. This study aimed to investigate adherence to ART among people living with HIV in northern Greece and investigate the factors influencing adherence to ART. METHODS A correlational study was performed on a cohort of 112 seropositive individuals (100 men and 12 women) with a mean age of 37.14 years. The simplified medication adherence questionnaire (SMAQ) was used to assess adherence. In addition, the perceived available support questionnaire (PAS) for social support assessment was utilized to evaluate the perceived social support. RESULTS Approximately 60% of patients were found to be nonadherent to ART. Important factors affecting adherence are educational level, social support, and use of substances. CONCLUSIONS The results show that a significant proportion of the cohort of patients investigated from northern Greece does not show adherence to ART. Several factors were identified to be of significant influence, which should be taken into consideration by the Greek healthcare providers. HIPPOKRATIA 2020, 24(3): 114-119.