Background: Young people (YP) with long-term conditions (LTCs) are at greater risk of psychological distress than those without LTCs. Despite this, there is a scarcity of quality digital interventions designed to help improve mental well-being in this population The aim of this study was to determine what YP, parents and health professionals preferred for future interventions. Methods: 26 YP with asthma, diabetes and/or epilepsy (the 3 most common LTCs in YP), 23 parents of YP with LTCs and 10 health professionals mainly in paediatric specialisms (total n= 59) took part in an online Delphi study to gain consensus (set at 75% agreement) on 4 questions across 3 rounds. Participants ordered psychological themes that may be experienced by YP with LTCs by importance and ranked digital intervention types and delivery modes by importance or usefulness. The most common results were reported if no consensus was reached by round 3. Results: Participants preferred a mobile phone app (73% agreement) and a mixture of one-on-one and group support for an intervention (75% agreement). The two highest ranked psychological themes were anxiety (44%) and wanting to appear normal (38%), and the top intervention type was ‘general counselling’ (54% agreement). Conclusion: There was a clear desire for an app to help with the psychological aspects of living with LTCs and for a combination of one-to-one and group intervention elements. Anxiety and wanting to appear ‘normal’ might be two closely linked psychological challenges that could be addressed by a single intervention. Implications: The results will be important to consider for a future intervention, although further consultation will be needed for app development. Patient or Public Contribution: 2 YP with a LTC provided feedback on the study protocol including the aims and procedures of the project. Another 6 YP with LTCs were consulted on an early draft of the study questionnaire (the 4 questions) which was subsequently revised. Once the project began, a PPI group consisting of two young people with LTCs and one parent of a YP with a LTC gave feedback on the research process, lay report of the results and dissemination plan.

A three-round electronic modified Delphi (eDelphi) study was used to gain consensus across all participants. A Delphi study refers to a process where participants are asked about an issue and the results of each round are reported to participants before the next round commences, until a consensus is met by all participants. Individuals meeting the following eligibility criteria were included in the study: 1) Young people aged 10 to 18 years old with one or more of the LTCs asthma, diabetes and epilepsy. 2) Parents or guardians of young people aged 11 to 18 years old with one or more of the LTCs asthma, diabetes and epilepsy 3) Professionals working with young people aged 11 to 18 years old with LTCs from the following fields: healthcare professionals (such as nurses, doctors and clinical psychologists), teachers and social workers Young people and parents/guardians were recruited via a newsletter, an online advert and an online public advisory board of eNurture, potentially reaching hundreds of young people and their families. To increase participation, we also used online adverts in school newsletters for two secondary schools in the Midlands, UK. These schools were independent (fee paying) and were part of the same network of schools. Professionals were recruited through workplaces including the secondary schools above (e.g., for school nurses and teachers) and existing contacts from within the research team, using snowball sampling.