This meta-analysis synthesized the proportion of adolescents and young adults (AYAs) who are adherent to pre-exposure prophylaxis (PrEP) and factors moderating adherence. A systematic search was conducted of studies published through May 2020 using PubMed, PsycInfo, Cochrane, EMBASE, and CINAHL. Included studies reported the proportion of AYAs (mean age ≤ 29 years) who were PrEP adherent. PrEP adherence was meta-analyzed using random-effects models. Secondary analyses evaluated potential moderating variables. A total of 41 individual samples, from 29 studies, of 8,679 AYA (weighted average age = 23.8 years) were synthesized. The proportion of AYA who met study-defined thresholds for PrEP adherence was .64 (95% confidence interval .57-.71) across studies. Subgroup analyses revealed that adherence was lower in young cisgender women (.46) than young men who have sex with men (.65) and serodiscordant heterosexual couples (.98). Adherence was higher in studies initiated after 2012 (.70) than earlier studies (.47). No differences based on participant age, country, or strategies to promote adherence were found. Across published studies to date, 64% of AYA demonstrate adequate PrEP adherence. Findings can be used to guide PrEP adherence interventions and also provide directions for future research on PrEP among AYA.