Although personal identities influence teaching and learning and the field of mathematics education is committed to equity and diversity for all learners, sexual minorities have been neglected in mathematics education research. Accordingly, the purpose of this paper is to call for research on sexual identity in mathematics education. I first define key terms and their relationships. Next, I discuss how students' sexual identity relates to school experiences and outcomes. I then summarize existing research on sexual identity and STEM/mathematics education. Finally, I recommend research on sexual identity and mathematics education that can advance our field in a continued commitment to equitable mathematics teaching and learning.