People experiencing mental health illnesses such as posttraumatic stress disorder (PTSD) who do not receive mental health treatment services (MHTS) are at a higher risk of committing crimes. The research problem of this study was to fill the gap in the literature concerning gender, sex at birth, and gender identity differences as predictors of attitudes toward perceived stigma in help-seeking behavior (HSB) and use of MHTS. The sample size included 5,000 participants in the de-identified secondary data set of students from 26 universities and colleges across the United States. The Healthy Minds Study collected these data in 2016-2017 using the Patient Health Questionnaire. To address the research questions guiding the study, one-way ANOVA was used to test for differences in groups based on sexual orientation and gender identity for measures of perception of stigma, use of MHTS, and HSB regarding receiving mental health services. Between groups, MANOVA was used to assess differences in groups based on gender identity and sexual orientation on a linear combination of the dependent measures of perception of stigma in use of MHTS and HSB. There were directional differences between groups based on independent variables gender and sexual orientation on measures of the dependent variables perception of stigma in use of MHTS and of HSB. However, a closer examination of the results indicated that the effect size associated with the directional differences was weak. The results from this study may help clinicians to identify treatment challenges related to biological sex and gender identity and help to influence future interventions to better accommodate the contemporary population of men and women experiencing symptoms of PTSD.