Objective Although cross-sectional studies have shown that the COVID-19 pandemic has negativelyaffected the mental health of adolescents, the effect of the pandemic on adolescents with pre-pandemicsymptoms is unclear. We therefore tested the hypothesis that adolescents had increased emotional andbehavioral problems during the lockdowns imposed during the pandemic.Method This study included three measurements in a prospective cohort of 1022 adolescentswho were oversampled based on their high risk of developing psychopathology. Before the pandemic, weassessed depressive, anxiety, stress, oppositional defiant problems, psychotic experiences and suicidality,using the Youth Self-Report; 445 and 333 of these 1022 adolescents subsequently completed the onlinequestionnaire in the first lockdown (in April 2020) and in the second lockdown (in January 2021),respectively. Multilevel random intercept regression models were used to determine the change inpsychiatric symptoms, including an interaction term to assess whether these changes differed based onthe severity of symptoms prior to the pandemic.Results Throughout the pandemic, the majority of adolescents reported having emotional and behavioralsymptoms that were within the normal range. Moreover, the mean symptom scores for all six outcomesdecreased significantly among adolescents with high clinical severity prior to the pandemic.Conclusion In contrast to our original hypothesis, the effects of the COVID-19 pandemic may notnecessarily be detrimental, at least among a specific subgroup of adolescents with preexisting mentalhealth problems. Moreover, our finding that most adolescents did not report experiencing clinicallyrelevant symptoms during the pandemic reflects their resilience during the pandemic.