Research has found that sexual orientation beliefs predict heterosexuals’ attitudes toward sexual minorities, and important sexual identity outcomes in sexual minority populations. To this point, no studies have systematically examined how sexual orientation beliefs may be associated with sexual identity self-labeling among sexual minority individuals. The present study examined this question in a sample of 1840 same-gender attracted individuals recruited for a cross-sectional online survey. Beliefs in the naturalness and discreteness of sexual orientation categories were highest in gay/lesbian individuals, intermediate in bisexual people, and lower in queer and pansexual individuals. Beliefs in the importance of sexual orientation were highest in gay/lesbian and queer identified individuals and lower in bisexual people. Within-group analysis demonstrated that gay/lesbian individuals who reported more exclusive same-gender attraction reported higher naturalness, discreteness, and importance beliefs than those with less-exclusive same-gender attraction. However, naturalness, discreteness, and importance beliefs were not associated with sexual attraction patterns in bisexual individuals. Finally, among predominately same-gender attracted populations, the adoption of a queer identity (over a gay/lesbian identity) was predicted by lower naturalness and discreteness beliefs, and increased perceived importance in females. Among non-monosexual populations, adoption of a pansexual identity over a bisexual identity was predicted by lower naturalness beliefs in females, but not predicted by sexual orientation beliefs in males. Collectively, these findings suggest that sexual orientation beliefs differ between sexual identity groups and may partly explain the adoption of particular sexual identity labels among contemporary sexual minority populations.