Background: Although significant associations of childhood adversities with adult mental disorders are widely documented, most studies focus on single childhood adversities predicting single disorders. Aims: To examine joint associations of 12 childhood adversities with first onset of 20 DSM-IV disorders in World Mental Health (WMH) Surveys in 21 countries. Method: Nationally or regionally representative surveys of 51 945 adults assessed childhood adversities and lifetime DSM-IV disorders with the WHO Composite International Diagnostic Interview (CIDI). Results: Childhood adversities were highly prevalent and interrelated. Childhood adversities associated with maladaptive family functioning (e.g. parental mental illness, child abuse, neglect) were the strongest predictors of disorders. Co-occurring childhood adversities associated with maladaptive family functioning had significant subadditive predictive associations and little specificity across disorders. Childhood adversities account for 29.8% of all disorders across countries. Conclusions: Childhood adversities have strong associations with all classes of disorders at all life-course stages in all groups of WMH countries. Long-term associations imply the existence of as-yet undetermined mediators.