AIM: The aim of this study was to assess the rate of antiretroviral therapy (ART) adherence and to identify any determinants among adult patients. METHODS: A cross-sectional study was conducted on 351 ART patients in the ART clinic of the University of Gondar referral hospital. Data were collected by a pretested interviewer-administered structured questionnaire from May to June 2014. Multivariate logistic regression was used to determine factors significantly associated with adherence. RESULTS: Of 351 study subjects, women were more predominant than men (64.4% versus 35.6%). Three hundred and forty (96.9%) patients agreed and strongly agreed that the use of ART is essential in their life, and approximately 327 (93.2%) disclosed their sero-status to family. Seventy-nine (22.5%) participants were active substance users. The level of adherence was 284 (80.9%). Three hundred forty-one (97.2%) respondents had good or fair adherence. Among the reasons for missing doses were forgetfulness (29 [43.3%]), missing appointments (14 [20.9%]), running out of medicine (9 [13.4%]), depression, anger, or hopelessness (4 [6.0%]), side effects of the medicine used (2 [3.0%]), and nonbelief in the ART (2 [3.0%]). The variables found significantly associated with non-adherence were age (P-value 0.017), employment (P-value 0.02), HIV disclosure (P-value 0.04), and comfortability to take ART in the presence of others (P-value 0.02). CONCLUSION: From this study, it was determined that forgetfulness (43.3%) was the most common reason for missing doses. Also, employment and acceptance in using ART in the presence of others are significant issues observed for non-adherence. Hence, the ART counselor needs to place more emphasis on the provision and use of memory aids.