Background Sexual minorities are more likely than their heterosexual counterparts to develop alcohol use disorder (AUD), and understanding the underlying reasons for this heightened risk is a public health priority. This study examined relationships between sexual orientation discrimination and DSM-5 AUD severity. Methods The 2012 to 2013 National Epidemiologic Survey on Alcohol and Related Conditions III conducted in-person interviews with a nationally representative sample of U.S. adults (N = 36,309). Approximately 2.8% of the target population self-identified as lesbian, gay, or bisexual, 3.1% had at least 1 past-year same-sex sexual partner, and 8.3% reported same-sex sexual attraction. Results Adults who identified as lesbian, gay, bisexual, heterosexual with same-sex attraction and/or current same-sex sexual partners, and those not sure of their sexual identity, had higher rates of individual DSM-5 AUD criteria than heterosexual-identified adults with only opposite-sex attraction and sexual partners. Respondents who were bisexual or unsure of their sexual identity consistently had the highest probabilities of endorsing each of these AUD criteria relative to the other subgroups. Differences in AUD severity across sexual orientation subgroups were much larger among women than among men. Sexual minorities who experienced higher levels of sexual orientation discrimination had significantly higher levels of AUD severity than sexual minorities who experienced lower levels or no discrimination. In particular, greater levels of sexual orientation discrimination increased the odds of impaired control criteria and pharmacologic criteria. Associations between prior-to-past-year sexual orientation discrimination and AUD severity were not as robust as those involving past-year discrimination. Conclusions Sexual minorities are at substantially greater risk of severe DSM-5 AUD, and this is particularly true among those who experience high levels of sexual orientation discrimination. Findings indicate that proximal experiences of discrimination are more salient than distal experiences. AUD treatment should address recent sexual orientation discrimination given that such experiences are associated with more severe AUD.