The Athletic Training Milestones were developed as a comprehensive framework to assess athletic trainers' knowledge, skill, and behavior acquisition across the continuum of athletic training practice. However, without established content validity, it is unclear whether the Athletic Training Milestones can be used effectively as a clinical evaluation and research tool to evaluate competence and performance across multiple users and sites. We conducted a highly conservative content validity index (CVI) with data from 12 content experts. Our findings revealed an extremely high overall scale CVI of 0.99, and CVI scores of the 28 individual subcompetency items assessed ranged from 0.83 to 1.00. For the athletic training profession to truly embrace competency-based evaluation and performance assessments, we need a highly valid and comprehensive instrument, such as the Athletic Training Milestones.