The COVID-19 pandemic has a great impact on society as a whole. Yet the pandemic and associated mandatory lockdown in several countries may have increased the vulnerability of certain populations. The present study aimed to document the frequency of clinical level of psychological distress and COVID-19 related post-traumatic stress symptoms in youth during the first wave of the pandemic. The study more specifically explored the role of prior trauma and adverse life events as a vulnerability factor for negative outcomes. A sample of 4914 adolescents and young adults from the province of Quebec, Canada was recruited online through social networks during the first wave of COVID-19. Results revealed that 26.6% of youth displayed serious psychological distress and 20.3% probable PTSD symptoms. The number of past traumas and adversity experienced showed a dose-response relation with the prevalence of psychological distress and PTSD. After controlling for socio-demographic characteristics and COVID-19 related variables (exposure, fear, suspicion of having the infection), participants with a history of five traumas and more presented a two-fold risk of serious psychological distress and probable PTSD. Emotion dysregulation was also associated with an increased risk of symptoms while resilience was linked to a reduced risk of distress.