Dutch version of the MWYS In the present multi-sample mixed method study, we developed a novel assessment tool of youth wellbeing, the Multidimensional Wellbeing in Youth Scale (MWYS). In Study 1, an online survey study among Dutch-speaking adolescents and young adults ( N = 339, M age = 18.44 years, SD = 3.53, 79 % females) was conducted to inspect which initial MWYS-items were viewed as being important for their wellbeing. In Study 2, we co-evaluated the original MWYS-items and co-created new items with adolescents and young adults ( N = 25) via focus groups. In Study 3, we examined the validity and reliability of the updated MWYS in a new sample of Dutch-speaking adolescents and young adults ( N = 239, M age = 19.68 years, SD = 4.40, 68 % females). Principal Components Analyses revealed five preliminary components of adolescent wellbeing: 1) having impact, purpose, and meaning; 2) dealing with stress and worry; 3) family relationships; 4) self-confidence; and 5) feeling respected, appreciated, and loved. These MWYS-components were related to other measures of mental health and wellbeing, and the MWYS showed good internal consistency and test-retest reliability. In conclusion, the MWYS was found to be a valid and reliable measure of youth wellbeing.