This report presents findings from the first harmonized multi-country survey of adverse childhood experiences (ACEs) among young adults (18–30) across the EU, Iceland and Norway, involving 26 741 respondents. More than two-thirds reported at least one ACE, with higher exposure linked to poorer mental and physical health, lower educational attainment and income, greater involvement in violence, and weaker social trust. ACEs were estimated to cause substantial losses in healthy life-years, while childhood resilience—particularly supportive adult relationships—mitigated these effects. The report calls for coordinated, trauma-informed, multisectoral policy action to prevent ACEs, build resilience, and break intergenerational cycles of adversity.