OBJECTIVE: To refine and evaluate the content validity of a bank of items representing the physical, social, and motivation behaviors associated with youth sport specialization. DESIGN: Qualitative analysis METHODS: The conceptual framework for item generation involved an existing consensus-based definition of youth sport specialization. Purposive sampling recruited English literate youth athletes who participated in at least one organized sport in the past 12 months to participate in individual cognitive interviews. Three rounds of interviews used a ‘read aloud; think aloud’ strategy to evaluate the comprehension, relevance, and comprehensiveness of the items and their response structure. One reviewer conducted thematic analysis of verbatim transcripts following rounds 1-2; after round 3, two independent reviewers evaluated the content validity of all items. The full research team reviewed results and established consensus regarding item acceptance, revision or removal. RESULTS: Twenty-two participants (64% male, 13.8±3.0 years) were interviewed. Participants were classified as low (59%), moderate (23%), and high (18%) specialization. Thirty-one items organized into participation volume, physical, motivation, and social domains were tested. Comprehension of 24 items in the physical (n=6), motivation (n=12), and social (n=6) domains was acceptable. No participation volume items achieved content validity. Acceptable items were considered relevant to youth sport specialization, and the item bank was deemed comprehensive. Participants affirmed the response structure was easy to understand and use. CONCLUSION: Content validity was established for a bank of patient-reported items assessing youth sport specialization. An appropriate next step is to conduct psychometric evaluation and develop a youth sport specialization assessment.