To identify and categorize barriers, facilitators, and strategies to boost exercise therapy adherence in youth with musculoskeletal conditions to inform research and clinical practice. Scoping review. We searched MEDLINE, CINAHL, SPORTDiscus, Scopus, PEDro, and ProQuest from inception to October 1, 2019. Studies written in English, with original data featuring an adherence barrier, facilitator, or boosting strategy for exercise therapy in youth (age, 19 years or younger) with musculoskeletal conditions, were included. Arksey and O'Malley's framework and the PRISMA Extension for Scoping Reviews guided data synthesis. Study quality was assessed with the Mixed Methods Appraisal Tool. Descriptive consolidation included study and sample characteristics, exercise therapy details, and adherence measurement specifics. Inductive thematic analysis of adherence barriers, facilitators, and boosting strategies followed Braun and Clarke's 6-step guide. Of 5705 potentially relevant records, 41 studies, representing 2020 participants (64% girls; age range, 2-19 years) with 12 different musculoskeletal conditions and multiple exercise therapy interventions, were included. Despite poor reporting of adherence concepts, time constraints, physical environment (eg, location), and negative exercise experiences were commonly identified barriers. Social support and positive exercise experiences were frequently identified facilitators. Reinforcement, exercise program modification, and education were recurring boosting strategies, despite being infrequent barriers or facilitators. A diversity of barriers to and facilitators of exercise therapy for youth with musculoskeletal conditions were identified. Efforts to link adherence-boosting strategies to an individual's needs should be considered. Making exercise enjoyable, social, and convenient may be important to maximizing adherence in this population. .