Research on the assessment of sexual orientation has been limited, and what does exist is often conflicting and confusing. This is largely due to the lack of any agreed upon definition of bisexuality. The Multidimensional Scale of Sexuality (MSS) was developed to validate and to contrast six proposed categories of bisexuality, as well as categories related to heterosexuality, homosexuality, and asexuality. This instrument includes ratings of the behavioral and cognitive/affective components of sexuality. The MSS was completed by 148 subjects, the majority of whom were from identified homosexual and bisexual populations. Although subjects' self-descriptions on the MSS were consistent with their self-descriptions on the Kinsey Heterosexual-Homosexual Scale, the MSS provided a more varied description of sexual orientation. Subject's self-described sexual orientation on the MSS was more consistent with their cognitive/affective ratings than with their behavioral ratings. With the exception of self-described heterosexuals, the frequency of cognitive/affective sexuality was greater than that of behavioral sexuality.