Background: For antiretroviral therapy (ART)to work effectively, adherence is very crucial.rnHowever, most of the studies done on ART adherence are either on children or on adults. Therernis limited information on the level of adherence among adolescents. Since the physical,rnbiological and behavioral changes which occur during adolescence could affect ART adherence,rnwe endeavored to assess the level of adherence among adolescents treated at three hospitals inrnAddis Ababa, Ethiopia.rnStudy Objective: This study was carried out to assess the magnitude of ART adherence amongrnHIV infected adolescents in Addis Ababa, Ethiopia. It also looked into the various sociodemographic,rnbehavioralrnandrnclinicalrnfactorsrnassociatedrnwithrnARTrnadherencernamongrnadolescents.rnStudy Methods: Using a cross-sectional study design, 273 HIV infected adolescents receivingrnART were interviewed from three hospitals in Addis Ababa. We used a structured questionnairernto measure adherence levels using patient self-reports among randomly selected adolescents agedrn13-19 years. Data was entered using Epi Info version 3.5.4 and exported to SPSS version 21 forrnanalysis. Bivariate and multivariate methods were used for analysis.rnResults: We interviewed 273 adolescents aged 13 to 19 years, and 144 (52.7%)of thernparticipants were female. Their mean age was 15.42 years (SDÂ± 1.75). The self-reportedrnadherence rate of the respondents was 79.1% (216/273). Most (96%)were on first line antiretroviralrndrugs. The median duration on ART was 7 years (IQR, 3). On Bivariate analysis; WHO stage, beingrnon Cotrimoxazole Prophylactic Therapy (CPT), marital and living status of the parent, whetherrnparent was on ART and having special instructions for ART medications were associated withrnoptimum adherence. However only WHO stage IV (adjusted OR, 12.874 95% CI, 2.079-79.706),rnbeing on CPT (adjusted OR, 0.339 CI, 0.124-0.97)and adolescents with widowed parent (AdjustedrnOR, 0.087 with CI, 0.021-0.359) were significantly associated with optimum adolescent ARTrnadherence.rnConclusions: The level of self-reported ART adherence among HIV infected adolescents at thernthree hospitals was below the recommended threshold. Being in advanced WHO clinical stagernwas associated with better adherence levels, but history of taking CPT was associated withrnpoorer adherence. Earlier presentation of adolescents to care should be encouraged, but morerntargeted adherence support should be planned for those who present at early stage of their illness.