Abstract: Sexual minority veterans are at heightened risk for mental health conditions compared with their heterosexual peers. Subpopulations of the sexual minority community, including veterans, are at even greater risk for mental health conditions. Despite this heightened risk, little is known about mental health treatment seeking among sexual minority veterans, especially in under-researched sexual minority subpopulations (e.g., bisexual men and women). This study examined sexual orientation-based differences in mental health symptom severity and past-year mental health treatment among a national sample of post-9/11 veteran men and women (N = 14,968). Results indicated that bisexual veteran women had greater mental health symptom severity compared with lesbian/gay and heterosexual veteran women. Gay and bisexual veteran men had greater depression and anxiety symptom severity than heterosexual veteran men. However, among individuals who reported receiving a mental health diagnosis (posttraumatic stress disorder, depression, anxiety) there were no significant differences in odds of receiving mental health treatment between lesbian/gay and bisexual veteran men and women compared to their heterosexual counterparts. These results suggest the need for additional research on facilitators and barriers to accessing and engaging in mental health care among sexual minority veterans, especially bisexual veteran women who experience disproportionate psychological burden compared to their lesbian/gay and heterosexual peers.