This study attempted to measure anti-retroviral therapy (ART) adherence level inrnZewditu Memorial Hospital, Addis Ababa. Retrospective and cross-sectionalrnsources were used. Patient self-report adherence measuring tool was used.rnBased on this structured Patient self-report adherence questionnaire and in arnsimple random sampling technique data were collected from 138 clinical recordsrnof ART patients, exit- interviews were conducted on 50 ART patients and fewrnART providers. Descriptive, one sample t-test, correlation, uni-variate andrnmultivariate logistic regression analysis were used. The findings revealed mixedrnadherence level (clinical data perspective 95-100% adherence rate found amongrn95% of the sample whereas in exit interview data analysis perspective 100%rnperfect adherence level was found among 30 respondents, suboptimal adherencernrate which ranges from 29% to 86% found among 19 individuals whereas, onernindividual had 0% adherence/he didnâ€™t took his ART for that week/. Waitingrnmonths on ART and regimen change were predictive factors for non-adherencernbehavior. Drug side effect/toxicity is a major reason for missed drug doses andrnregimen changing behavior. Forgetting, being busy, social stigma orrndiscrimination, and alcohol use were the identified barriers for non- adherencernbehavior. Finally the study hints the necessity to design and practicallyrnimplement substantive theories of behaviors based adherence interventionsrnprogrammes that can promote adherence behaviors and alleviate the burdens ofrnstigma or discrimination and drug side effects among ART patients.