Aims To assess past-year prevalence rates of substance use behaviors and substance dependence across three major dimensions of sexual orientation (identity, attraction and behavior) in a large national sample of adult women and men in the United States. Design Data were collected from structured diagnostic face-to-face interviews using the Alcohol Use Disorder and Associated Disabilities Interview Schedule DSM-IV version IV (AUDADIS-IV). Setting Prevalence estimates were based on data collected from the 2004?2005 (wave 2) National Epidemiologic Survey on Alcohol and Related Conditions (NESARC). Participants A large national sample of 34 653 adults aged 20 years and older: 52% female, 71% white, 12% Hispanic, 11% African American, 4% Asian and 2% Native American. Findings Approximately 2% of the population self-identified as lesbian, gay or bisexual; 4% reported at least one life-time same-sex sexual partner and 6% reported same-sex sexual attraction. Although non-heterosexual orientation was generally associated with a higher risk of substance use and substance dependence, the majority of sexual minority respondents did not report substance use or meet criteria for DSM-IV substance dependence. There was considerable variation in substance use outcomes across sexual orientation dimensions; these variations were more pronounced among women than among men. Conclusions Results support previous research findings of heightened risk of substance use and substance dependence among some sexual minority groups and point to the need for research that examines the reasons for such differences. Results also highlight important gender differences and question previous findings indicating uniformly higher risk for substance dependence among sexual minorities. Risks appear to vary based on gender and how sexual orientation is defined. Findings have implications for more effective prevention and intervention efforts that target subgroups at greatest risk.