Previous studies have established a core outcome set for paediatric chronic pain clinical trials. The aim of this research was to establish which outcomes young people and parents considered important to measure during treatment for chronic musculoskeletal pain. To the best of our knowledge, this is the first study to explore which outcomes could be used to tailor interventions within a clinical setting. Twenty-one young people (age 11-18 years) and twenty-one parents were recruited from two UK hospital sites and took part in semi-structured interviews that incorporated drawing a timeline of their treatment. They identified positive and negative outcomes showing the perceived effectiveness of treatment. Informed by Q methodology, the words and phases of young people and parents were developed into 101 statements that were mapped onto the core outcome set and represented wide-ranging opinions regarding the outcomes they considered important (Q set). This approach helped identify additional statements related to ‘parent and family functioning’ not routinely considered. Outcomes related to the treatment experience and adverse effects were highlighted as important, yet are not routinely prioritised in clinical research. Parents prioritised outcomes related to the treatment experience, whereas young people prioritised their overall wellbeing. Over the course of treatment, outcome focus changed, with some outcomes only deemed relevant at a specific time point. Overall, the research highlighted the need for clinical guidance on which outcome domains to measure during the treatment course to gauge treatment effectiveness and optimally tailor interventions. PERSPECTIVE: This study established the range of outcomes that were important to young people and their parents during treatment for chronic musculoskeletal pain. The findings show how young people and parents have different outcome preferences and how their outcome focus changes during the treatment course.Copyright © 2024. Published by Elsevier Inc.