This study presents data on the prevalence, impairment, and demographic correlates of major depressive episodes (MDE) from 18 countries participating in the World Mental Health Survey Initiative. The average lifetime and 12-month prevalence estimates of DSM-IV MDE were 14.6% and 5.5% in high-income countries, and 11.1% and 5.9% in low- to middle-income countries. The average age of onset was 25.7 years in high-income countries and 24.0 years in low- to middle-income countries. Functional impairment was associated with the recency of MDE, and the female-to-male ratio was about 2:1. In high-income countries, younger age was associated with higher 12-month prevalence, while in several low- to middle-income countries, older age was associated with greater likelihood of MDE. The strongest demographic correlate in high-income countries was being separated from a partner, and in low- to middle-income countries, it was being divorced or widowed. The study concludes that MDE is a significant public health concern across all regions and is strongly linked to social conditions, with future research needed to investigate the specific demographic risk factors in different countries.This study presents data on the prevalence, impairment, and demographic correlates of major depressive episodes (MDE) from 18 countries participating in the World Mental Health Survey Initiative. The average lifetime and 12-month prevalence estimates of DSM-IV MDE were 14.6% and 5.5% in high-income countries, and 11.1% and 5.9% in low- to middle-income countries. The average age of onset was 25.7 years in high-income countries and 24.0 years in low- to middle-income countries. Functional impairment was associated with the recency of MDE, and the female-to-male ratio was about 2:1. In high-income countries, younger age was associated with higher 12-month prevalence, while in several low- to middle-income countries, older age was associated with greater likelihood of MDE. The strongest demographic correlate in high-income countries was being separated from a partner, and in low- to middle-income countries, it was being divorced or widowed. The study concludes that MDE is a significant public health concern across all regions and is strongly linked to social conditions, with future research needed to investigate the specific demographic risk factors in different countries.