OBJECTIVES: We examined the relation between living in states that instituted bans on same-sex marriage during the 2004 and 2005 elections and the prevalence of psychiatric morbidity among lesbian, gay, and bisexual (LGB) populations. METHODS: We used data from wave 1 (2001-2002) and wave 2 (2004-2005) of the National Epidemiologic Survey on Alcohol and Related Conditions (N = 34,653), a longitudinal, nationally representative study of noninstitutionalized US adults. RESULTS: Psychiatric disorders defined by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, increased significantly between waves 1 and 2 among LGB respondents living in states that banned gay marriage for the following outcomes: any mood disorder (36.6% increase), generalized anxiety disorder (248.2% increase), any alcohol use disorder (41.9% increase), and psychiatric comorbidity (36.3% increase). These psychiatric disorders did not increase significantly among LGB respondents living in states without constitutional amendments. Additionally, we found no evidence for increases of the same magnitude among heterosexuals living in states with constitutional amendments. CONCLUSIONS: Living in states with discriminatory policies may have pernicious consequences for the mental health of LGB populations. These findings lend scientific support to recent efforts to overturn these policies.