Purpose: To develop a Thai questionnaire ชีวิตและสุขภาพของวัยรุ่นในประเทศไทย (TYQ) to explore girls’ and boys’ living conditions, lifestyles and self-reported health with special focus on sexuality, based on a Swedish questionnaire Liv & Hälsa ung (SYQ). Challenges in developing a youth questionnaire for comparative studies are described. Design: A multi-step translation, socio-cultural adaptation procedure and a mixed-method validation test were performed using English as a common language within the research group. Three versions of SYQ were used as a pool of questions to develop the questionnaire. Findings: From a field-test, unclear questions were identified and minor adjustments made. Life & Health Young people in a Thai version was successfully developed. The English version was used to bridge the language gap. Conclusion: This unique multi-step methodology, including mixed-method validation procedure, can be used by researchers in countries where English is not the main language.