Background: Advocates of expanded mental health treatment assert that mental disorders are as disabling as physical disorders, but little evidence supports this assertion. Aims: To establish the disability and treatment of specific mental and physical disorders in high-income and low- and middle-income countries. Method: Community epidemiological surveys were administered in 15 countries through the World Health Organization world Mental Health (WMH) Survey Initiative. Results: Respondents in both high-income and low- and middle-income countries attributed higher disability to mental disorders than to the commonly occurring physical disorders included in the surveys. This pattern held for all disorders and also for treated disorders. Disaggregation showed that the higher disability of mental than physical disorders was limited to disability in social and personal role functioning, whereas disability in productive role functioning was generally comparable for mental and physical disorders. Conclusions: Despite often higher disability, mental disorders are undertreated compared with physical disorders in both high-income and in low- and middle-income countries.