Childhood adversities are strongly associated with adult mental disorders, as shown in the WHO World Mental Health Surveys. The study examined the joint associations of 12 childhood adversities with the first onset of 20 DSM-IV disorders across 21 countries. The surveys involved 51,945 adults, with childhood adversities and mental disorders assessed using the WHO Composite International Diagnostic Interview (CIDI). Childhood adversities were highly prevalent and interrelated, with those associated with maladaptive family functioning (e.g., parental mental illness, child abuse, neglect) being the strongest predictors of mental disorders. These adversities had significant subadditive predictive associations and little specificity across disorders, accounting for 29.8% of all disorders across countries. The study found that childhood adversities associated with maladaptive family functioning had consistently higher odds ratios than other adversities. Odds ratios for the number of such adversities were consistently negative and inversely related to the number of adversities. The results showed that childhood adversities significantly predict the first onset of all classes of disorders in all groups of countries. The population-attributable risk proportions (PARPs) indicated that eliminating childhood adversities could reduce the prevalence of mood disorders by 22.9%, anxiety disorders by 31.0%, behavior disorders by 41.6%, and substance disorders by 27.5%, with 29.8% of all disorders. The study also found that the effects of childhood adversities varied by life-course stage, with the strongest associations observed in childhood and adolescence. The results suggest that early intervention to reduce exposure to childhood adversities and later intervention to address long-term adult consequences could be effective. However, the study had limitations, including variations in survey methods, underrepresentation of rural areas, and the exclusion of some childhood adversities in certain countries. Additionally, the surveys did not assess psychosis, and retrospective recall bias may have led to underreporting of both childhood adversities and disorders. The findings support the importance of addressing childhood adversities to prevent adult mental disorders. The study highlights the need for further research to explore mediators, modifiers, and developmental sequences that could be targeted for preventive interventions. The results also emphasize the importance of early detection and intervention for severe childhood adversities, such as physical and sexual abuse and neglect. The study provides empirical justification for further analyses to identify these factors and improve mental health outcomes.Childhood adversities are strongly associated with adult mental disorders, as shown in the WHO World Mental Health Surveys. The study examined the joint associations of 12 childhood adversities with the first onset of 20 DSM-IV disorders across 21 countries. The surveys involved 51,945 adults, with childhood adversities and mental disorders assessed using the WHO Composite International Diagnostic Interview (CIDI). Childhood adversities were highly prevalent and interrelated, with those associated with maladaptive family functioning (e.g., parental mental illness, child abuse, neglect) being the strongest predictors of mental disorders. These adversities had significant subadditive predictive associations and little specificity across disorders, accounting for 29.8% of all disorders across countries. The study found that childhood adversities associated with maladaptive family functioning had consistently higher odds ratios than other adversities. Odds ratios for the number of such adversities were consistently negative and inversely related to the number of adversities. The results showed that childhood adversities significantly predict the first onset of all classes of disorders in all groups of countries. The population-attributable risk proportions (PARPs) indicated that eliminating childhood adversities could reduce the prevalence of mood disorders by 22.9%, anxiety disorders by 31.0%, behavior disorders by 41.6%, and substance disorders by 27.5%, with 29.8% of all disorders. The study also found that the effects of childhood adversities varied by life-course stage, with the strongest associations observed in childhood and adolescence. The results suggest that early intervention to reduce exposure to childhood adversities and later intervention to address long-term adult consequences could be effective. However, the study had limitations, including variations in survey methods, underrepresentation of rural areas, and the exclusion of some childhood adversities in certain countries. Additionally, the surveys did not assess psychosis, and retrospective recall bias may have led to underreporting of both childhood adversities and disorders. The findings support the importance of addressing childhood adversities to prevent adult mental disorders. The study highlights the need for further research to explore mediators, modifiers, and developmental sequences that could be targeted for preventive interventions. The results also emphasize the importance of early detection and intervention for severe childhood adversities, such as physical and sexual abuse and neglect. The study provides empirical justification for further analyses to identify these factors and improve mental health outcomes.