INTRODUCTION: World health organization defined adherence as the extent to which a person's behavior - taking medications, following a diet, or executing lifestyle changes correspond with agreed recommendations from the health care provider. There is a contradiction among studies and previous studies conducted in the study area used a cross-sectional study design. This study aimed to identify determinant factors for adherence to antiretroviral treatment among people living with HIV at Dessie Referral Hospital by using an unmatched case-control study design. METHODS AND MATERIALS: an institution-based unmatched case-control study design was used on a total sample of 582 (146 controls and 436 cases). Each respondent was selected by consecutive random sampling. The collected data were entered and analyzed by using Statistical Package for Social Science version 25.0. Multivariable binary logistic regression analysis was used to identify variables that were statistically significant determinants. RESULT: The mean age of the respondents was 41.64 years. About 61.5% of the participants were females. Patients with baseline HIV stage I was more likely to be adherent to the prescribed HIV medicine (AOR: 2.194 95% CI: 1.116, 4.314) as compared with those with baseline WHO stage IV. Patients who did not take anti-tuberculosis medication collaterally with the prescribed HIV medicine were more likely to be adherent (AOR: 2.271 95% CI: 1.257, 4.102). Patients who took antiretroviral therapy for more than 24 months were more likely to be adherent (AOR: 3.665 95% CI: 1.321, 10.170). CONCLUSION: Initiation of antiretroviral therapy at the later stage of the disease and taking anti-tuberculosis concomitantly were negatively associated with adherence. Being on antiretroviral therapy for a longer duration has a positive association. Health facilities and professionals should strictly apply strategies for the prevention of tuberculosis among HIV patients to avoid concomitant use of anti-tuberculosis medications.