Objective: The Health Behaviour in School-aged Children (HBSC) study is a World Health Organization collaborative cross-national research project which aims to improve understanding of young people’s health and wellbeing, including sexual behaviours. Data are collected on a four year cycle from schoolchildren in 43 countries in Europe and North America. Requests for detailed information about adolescent sexual behaviours have prompted the development of new sexual behaviour questions for use in the HBSC study. The aim of this pilot study was to provide guidance on the utility and appropriateness of new sexual health items for inclusion in future HBSC studies. Design and Method: A pilot involving 233 Irish students aged 15-19 years used questionnaires and classroom discussion groups to test the utility and appropriateness of new sexual health items. Twenty-one sexual behaviour questions were developed based on previously validated questionnaires. Questions measured sexual behaviour, romantic experiences and the circumstances surrounding first intercourse. Results: The findings provide feedback on the following dimensions of the proposed items; cultural acceptability, understandability, answerability, skews, translatability, relevance and contextual understanding. A test-retest provides further details on the validity and consistency of the questions. Analysis highlights questions which not only have conceptual cohesion within the study and the potential to inform policy but which are understandable, acceptable and of a high priority to the target population. Conclusions: The findings have provided guidance for the mandatory and optional sexual behaviour questions for further HBSC studies. They have informed a standardized protocol which will enable the collection of internationally comparable adolescent sexual behaviour data.