Background:Adherence to Highly Active Antiretroviral Therapy (HAART) medication is the pressing public health problem worldwide. Non-adherence to HAART leads to treatment failure, immunologic failure, and virological failure. Despite different interventions made; still, HAART medication adherence among adult people living with HIV/AIDS (PLWHA) is inconsistent across studies and the effect of HIV disclosure status was not well studied. Therefore this study determines the pooled prevalence of HAART adherence and its relationship with HIV disclosure status among Adult PLWHA.MethodsWe searched 3247 both published and unpublished original articles from January 2016 to November 2019 in Ethiopia using different search engines. Data were extracted using Microsoft excel. New Castle Ottawa Scale quality assessment tool was used. STATA software version 11 was used for analysis. A random-effects meta-analysis was performed. Cochran Q statistics and I2 were used to estimate heterogeneity. Eggers and Beggâs test was used to assess the publication bias.ResultsA total of 15 studies for systematic review and four studies for Meta-analysis were used. The pooled prevalence of HAART medication adherence is found to be 81.19% (80.132, 82.248). In the subgroup analysis, the pooled prevalence of HAART adherence was 79.82% (73.19, 86.45) in the Oromia region, 82.51% ( 73.14, 91.87) in the Amhara region, and 72.7% (63.78, 81.61) in the SNNPR. HIV disclosure improves HAART adherence by nearly three times compared to non-HIV disclosed HAART users (AOR=2.99, 95%CI: 1.88, 4.77).Conclusionsï»żThe pooled prevalence of HAART adherence among adult PLWHA was found to be low. Having HIV disclosure improved HAART medication adherence.