Abstract Introduction Prior studies report nicotine/tobacco use disparities for sexual and gender minority (SGM) youth but have insufficiently characterized SGM identity diversity. Aims and Methods Adolescents (mean age = 15.2) from 11 high schools in Southern California completed surveys in Fall 2021. Ever use of combustible (cigarettes, cigars, hookah) and noncombustible (e-cigarettes, e-hookah, heated tobacco, smokeless/snus, oral nicotine) nicotine/tobacco (among overall sample, n = 3795) and susceptibility to future initiation of cigarettes, e-cigarettes, and flavored non-tobacco oral nicotine (among n = 3331 tobacco-naïve youth) were compared across four gender (male/masculine, female/feminine, transgender male/female, non-binary) and seven sexual (heterosexual, bisexual, pansexual, queer, questioning, gay/lesbian, asexual) identities. Results Non-binary (vs. cisgender male) youth had greater prevalence of ever combustible (prevalence ratio [PR] = 2.86, 95% confidence intervals (CI): 1.76 to 4.66) and non-combustible (PR = 1.94, 95% CI: 1.31 to 2.86) nicotine/tobacco use, and susceptibility to future nicotine/tobacco initiation (PR range = 2.32–2.68). Transgender (vs. cisgender male) youth had greater susceptibility to nicotine/tobacco use (PR range = 1.73–1.95), but not greater tobacco use prevalence. There was greater prevalence of non-combustible nicotine/tobacco use (PR range = 1.78–1.97) and susceptibility to nicotine/tobacco initiation (PR range = 1.36–2.18) for all sexual minority (vs. heterosexual) identities, except for asexual. Bisexual (PR = 2.03, 95% CI: 1.30 to 3.16) and queer (PR = 2.87, 95% CI: 1.31 to 6.27) youth had higher ever combustible tobacco use than heterosexual youth. Questioning (vs. heterosexual) youth were more susceptible to future tobacco initiation (PR range = 1.36–2.05) but did not differ in ever use. Conclusions Disparities in nicotine/tobacco use and susceptibility were present with similar effect sizes across most, but not all, SGM identities. Inclusive measurement of SGM identities in research and surveillance may inform more precise tobacco control efforts to reduce disparities. Implications Among high school students from Southern California with substantial diversity in sexual and gender identities, there was greater prevalence of tobacco use and susceptibility to future tobacco initiation for most, but not all, sexual and gender minority youth, including those with emerging sexual and gender identities such as non-binary, queer and pansexual. Additionally, findings indicate that tobacco control initiatives targeting youth who are questioning their sexual identities may be particularly important for preventing tobacco use initiation. This study reinforces the importance of measuring diversity within the LGBTQ + community for tobacco use research, and highlights how inclusive measurement can inform more precise tobacco control interventions.