INTRODUCTION: Evidence on the real-world effects of "Treat All" on attrition has not been systematically reviewed. We aimed to review existing literature to compare attrition 12 months after antiretroviral therapy (ART) initiation, before and after "Treat All" was implemented in Sub-Saharan Africa and describe predictors of attrition. METHODS: We searched Embase, Google Scholar, PubMed, and Web of Science in July 2020 and created alerts up to the end of June 2023. We also searched for preprints and conference abstracts. Two co-authors screened and selected the articles. Risk of bias was assessed using the modified Newcastle-Ottawa Scale. We extracted and tabulated data on study characteristics, attrition 12 months after ART initiation, and predictors of attrition. We calculated a pooled risk ratio for attrition using random-effects meta-analysis. RESULTS: Eight articles and one conference abstract (nine studies) out of 8179 screened records were included in the meta-analysis. The random-effects adjusted pooled risk ratio (RR) comparing attrition before and after "Treat All" 12 months after ART initiation was not significant [RR = 1.07 (95% Confidence interval (CI): 0.91-1.24)], with 92% heterogeneity (I). Being a pregnant or breastfeeding woman, starting ART with advanced HIV, and starting ART within the same week were reported as risk factors for attrition both before and after "Treat All". CONCLUSIONS: We found no significant difference in attrition before and after "Treat All" one year after ART initiation. While "Treat All" is being implemented widely, differentiated approaches to enhance retention should be prioritised for those subgroups at risk of attrition. PROSPERO NUMBER: CRD42020191582 .