Juvenile idiopathic arthritis is an autoimmune condition of multifactorial etiology resulting in chronic inflammatory joint disease, which may be associated with systemic manifestations. Therapeutic exercise is essential to counteract physical impairments, which requires the implementation of outcome measures (OMs) in research and practice as they provide meaningful results for research efficacy, exercise program evaluation and quality, medication tolerance, and patient improvement. To assess the types of OMs implemented in exercise randomized controlled trials related to the juvenile idiopathic arthritis cohort and the psychometric properties and age appropriateness of the implemented OMs. The review was registered with PROSPERO (CRD42022336345) on May 30, 2022, followed by a systematic search across PubMed, EBSCOhost, Web of Science, and Ovid. Studies included were appraised using the Joanna Briggs Critical Appraisal Tool for randomized controlled trials. All data collection occurred according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis. A total of 51 outcome measures were implemented across the 20 randomized controlled trials: 2 clinician-reported OMs (4%), 19 patient or parent-reported OMs (37%), and 30 physical performance OMs (59%). The vast majority of included OMs increase the difficulty of comparison across studies and indicate a lack of consideration for validity, reliability, and age appropriateness.