CONTEXT: Gender differences in mental disorders, including more anxiety and mood disorders among women and more externalizing disorders among men, are found consistently in epidemiological surveys. The gender roles hypothesis suggests that these differences narrow as the roles of women and men become more equal. OBJECTIVES: To study time-space (cohort-country) variation in gender differences in lifetime DSM-IV mental disorders across cohorts in 15 countries in the World Health Organization World Mental Health Survey Initiative and to determine if this variation is significantly related to time-space variation in female gender role traditionality as measured by aggregate patterns of female education, employment, marital timing, and use of birth control. DESIGN: Face-to-face household surveys. SETTING: Africa, the Americas, Asia, Europe, the Middle East, and the Pacific. PARTICIPANTS: Community-dwelling adults (N = 72,933). MAIN OUTCOME MEASURES: The World Health Organization Composite International Diagnostic Interview assessed lifetime prevalence and age at onset of 18 DSM-IV anxiety, mood, externalizing, and substance disorders. Survival analyses estimated time-space variation in female to male odds ratios of these disorders across cohorts defined by the following age ranges: 18 to 34, 35 to 49, 50 to 64, and 65 years and older. Structural equation analysis examined predictive effects of variation in gender role traditionality on these odds ratios. RESULTS: In all cohorts and countries, women had more anxiety and mood disorders than men, and men had more externalizing and substance disorders than women. Although gender differences were generally consistent across cohorts, significant narrowing was found in recent cohorts for major depressive disorder and substance disorders. This narrowing was significantly related to temporal (major depressive disorder) and spatial (substance disorders) variation in gender role traditionality. CONCLUSIONS: While gender differences in most lifetime mental disorders were fairly stable over the time-space units studied, substantial intercohort narrowing of differences in major depression was found to be related to changes in the traditionality of female gender roles. Additional research is needed to understand why this temporal narrowing was confined to major depression.