We examined prevalence of mental health treatment utilization among 447 lesbian, gay, bisexual, transgender, and Two-Spirit (LGBTT-S) American Indian/Alaska Native (AI/AN) adults and the association of mental health treatment utilization with socio-demographic factors, social support, and mental health diagnoses. We derived data from the HONOR Project, a multi-site cross-sectional survey of Native LGBTT-S adults from seven U.S. metropolitan cities. Rates of lifetime mental health treatment utilization were higher for women (87%), those who were college educated (84%), and homeowners (92%). Cisgender women and transgender AI/AN adults had a higher prevalence than cisgender men of major depression, generalized anxiety, and panic disorder. Rates of subthreshold and threshold posttraumatic stress disorder were significantly higher for transgender adults. Lower positive social support and higher emotional social support were associated with greater odds of mental health treatment utilization. Mental health diagnoses and lifetime mental health treatment utilization was positively associated.