•LGB opioid disparities varied significantly by sexual identity and gender.•LGB women and gay men had elevated rates of past-year opioid misuse.•Lifetime heroin use was elevated among LGB women and bisexual men.•LGB women reported lower perceived risk of trying heroin and greater heroin access.•Bisexual women uniquely had elevated OUD rates and lifetime injection heroin use. Lesbian, gay and bisexual (LGB) adults have elevated use of many substances compared to heterosexual adults, yet LGB disparities in specific types of opioid misuse and perceived opioid risk have not been fully characterized. Data on 126,463 adults (including 8241 LGB adults) were from the 2015–2017 National Survey of Drug Use and Health. Logistic regression was used to estimate lesbian/gay (L/G) and bisexual disparities (relative to same-gender heterosexuals) for: lifetime prescription pain reliever misuse, heroin use and injection heroin use; past-year opioid misuse and opioid use disorder (OUD); and perceived risk of and access to heroin. All LGB subgroups had elevated lifetime pain reliever misuse rates relative to same-gender heterosexuals. Lifetime heroin use was elevated among LGB women and bisexual men; bisexual women had 4 times the odds of injection heroin use. LGB women and gay men had 1.4–2.4 times the odds of past-year opioid misuse; bisexual women had 2.5 times the odds of OUD. LGB women reported both lower perceived risk of trying heroin and greater perceived heroin access. Lifetime and past-year opioid misuse is elevated among LGB adults. Bisexual women are particularly at-risk, uniquely exhibiting disparities on high-risk injection use and OUD. Lower perceived risk of and greater access to heroin among LGB women may play a role in the onset or continuation of opioid misuse. Opioid misuse disparities among LGB adults are of substantial concern given the resultant elevated risk for fatal and non-fatal opioid overdose.