Research has found that non-monosexual women report worse mental health than their heterosexual and lesbian counterparts. The reasons for these mental health discrepancies are unclear. This study investigated whether higher levels of child abuse and risky sexual behavior, and lower levels of sexual orientation disclosure, may help explain elevated symptoms of depression and anxiety among non-monosexual women. Participants included 388 women living in Canada (Mean age = 24.40, SD = 6.40, 188 heterosexual, 53 mostly heterosexual, 64 bisexual, 32 mostly lesbian, 51 lesbian) who filled out the Beck Depression and Anxiety Inventories as part of an online study running from April 2011 to February 2014. Participants were collapsed into non-monosexual versus monosexual categories. Non-monosexual women reported more child abuse, risky sexual behavior, less sexual orientation disclosure, and more symptoms of depression and anxiety than monosexual women. Statistical mediation analyses, using conditional process modeling, revealed that sexual orientation disclosure and risky sexual behavior uniquely, but not sequentially, mediated the relation between sexual orientation, depression and anxiety. Sexual orientation disclosure and risky sexual behavior were both associated with depression and anxiety. Childhood abuse did not moderate depression, anxiety, or risky sexual behavior. Findings indicate that elevated levels of risky sexual behavior and deflated levels of sexual orientation disclosure may in part explain mental health disparities among non-monosexual women. Results highlight potential targets for preventive interventions aimed at decreasing negative mental health outcomes for non-monosexual women, such as public health campaigns targeting bisexual stigma and the development of sex education programs for vulnerable sexual minority women, such as those defining themselves as bisexual, mostly heterosexual, or mostly lesbian.