Theoretical Background: Positive mental health is not simply the absence of a mental disorder. We need a better understanding of the development of mental health, particularly if we are to better understand prevention, remission, and relapse in the context of mental disorders. To date, no measurement tool exists that captures positive mental health for childhood and adolescence, building on a robust theory of positive mental health. Objective: This study develops a questionnaire to assess positive mental health in children and adolescents between 6 and 18 years of age, both in self-report and in external report, and analyzes its quality in a first small sample. Method: Based on established adult scales, we developed a new questionnaire. 83 children and adolescents aged 6 – 18 years ( M = 11.89, SD = 3.0; 66 % female) and 77 parents completed the new questionnaire and other questionnaires assessing positive mental health and psychopathology. Results: The questionnaire showed a unidimensional factor structure as well as very good internal consistency and test-retest reliability. High positive correlations with self-efficacy and life satisfaction as well as high negative correlations with anxiety and depression confirmed the very good construct validity, both in child and parent ratings. Discussion and Conclusion: The PMH-Kids provides evidence of excellent psychometric quality in this first evaluation attempt. The questionnaire is comparable to its adult pendant, enabling researchers to assess positive mental health across the lifespan.