Introduction Adolescents have to cope with several challenges and restrictions due to the COVID-19 pandemic, with many of those incongruent with the typical developmental tasks of adolescent age. Some adolescent might be particularly vulnerable in this situation. Objectives This study aimed: 1) to collect data on the mental health and quality of life of adolescents during/after the pandemic; 2. to improve adolescents' mental health by providing an online prevention program that addresses their

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... ctual needs; 3. to accelerate the development of culturally adapted prevention programs by involving an international team, and 4. to contribute to adequate preparation for any similar situation in the future. Methods Participants aged 11-18 years and their parents/caregivers were recruited online. Data has been collected regularly in a follow-up study by Inventar zur Erfassung der Lebensqualitat and Strengths and Difficulties Questionnaire. The baseline data collection was in March 2020 at first restrictions of the COVID pandemic in Europe Results In the baseline data 428 adolescents (29.7% boys;70.3% girls) were included. Adolescents reported significantly lower quality of life during the pandemic (F (1,557) = 29.11; p <0.001; R2 = 0.048). There was no significant difference in quality of life according to whether the adolescents live in a household with their siblings ( F (2, 356) = 0.785 p = 0.457; η2 = 0.004), and whether the adolescents have symptoms of hyperactivity (ß = 0.105; p = 0.295). Conclusions Prevention based on the results of this study is expected to contribute to maintaining adolescents' mental health during and after the COVID pandemic. Disclosure No significant relationships.