Background We lack appropriate person-centred outcome measurement (PCOM) to direct and evaluate care. Methods In line with COSMIN measure construction guidance, we convened an expert group to elicit views on 1) domains/items to include; 2) implementation challenges; 3) requirements for use in routine care by practitioners. Data were content analysed. Results N=36 UK-wide clinicians, advocates, and researchers participated. 1) Items for inclusion were: specific symptoms, education, play and social interaction, parental time for partner & other children, sex & intimacy, and sibling wellbeing. 2) Implementation challenges: supporting CYP to engage meaningfully, the instrument being seen as a "test" of parents' care quality, raising unrealistic expectations, proxy validity. 3) Need for clear administration and interpretation guidance, agreeing data ownership/access. Conclusions This expert meeting addressed the initial step in COSMIN guidance, informing face validity and acceptability. It provides the information necessary for the first phase of tool development and informs potential utility and implementation. Specialised services [Online]. NHS England. Available: http://www.england.nhs.uk/commissioning/spec-services/ [Accessed 07/08/15]. 2015. Towards the development of outcome measures for children and young people with lifelimiting and life-threatening conditions. ANTUNES, B., HARDING, R. & HIGGINSON, I. J. 2014. Implementing patient-reported outcome measures in palliative care clinical practice: a systematic review of facilitators and barriers.