BACKGROUND: Recap of atopic eczema (RECAP) is a patient-reported outcome measure (PROM) assessing eczema control. This instrument has been developed and validated in the UK. There is a self-reported and a proxy-reported version in English, Dutch and German. However, it is unclear whether the self-reported version shows adequate content validity when completed by young people (8-16 years) in these languages. OBJECTIVES: To assess the content validity (comprehensibility, relevance and comprehensiveness) of the English, German and Dutch versions of the self-reported RECAP in young people with atopic eczema and to identify the most appropriate age cut-off for self-completion. METHODS: We conducted 23 semi-structured cognitive interviews with young people from 8 to 16 years, using the "think-aloud" method. In Germany and the Netherlands, participants were recruited in dermatology clinics and in the UK through social media and existing mailing lists. Interviews were audio recorded, transcribed verbatim and analysed in the three languages, using a problem-focused coding manual. Transcripts were coded by two independent reviewers in each country. Themes were translated into English and compared across the three countries. RESULTS: Significant age-related comprehensibility issues with the last three items of the questionnaire occurred with young people aged 8 to 11 years, causing difficulties completing RECAP without help. However, older children had only minor problems and were able to complete the questionnaire by themselves. The self-reported version of RECAP has sufficient content validity for self-completion in young people aged 12 years and above. However, the German version with some translational adaptations may be appropriate for children from the age of 8 years. There may be some situations, where the proxy-version is needed for older children too. CONCLUSIONS: The self-reported version of RECAP is appropriate for use from the age of 12 years. The proxy-version can be used in children younger than 12 years. ...