Researchers have begun to explore and identify various gradations in sexual orientation identity, paying attention to alternative sexual identity categories and attempting to clarify potential subtypes of same-sex sexuality, particularly among women. This study utilizes both quantitative and qualitative data to explore the behavioral experiences and identity development processes among women of a particular sexual identity subtype, "mostly straight." Participants were 349 female college students whose primary sexual identities included exclusively straight, mostly straight, bisexual, and lesbian. Results indicated that, on most behavioral variables, mostly straight women fell directly between and were significantly different from exclusively straight and bisexual/lesbian women. Mostly straight women were also distinct from exclusively straight women but were similar to bisexual women and lesbians on several quantitative measures of identity. Narratives about sexual identity development for mostly straight women revealed the complexities of sexual identity exploration, uncertainty, and commitment within this population. As a whole, this study encourages researchers to begin to recognize and examine mostly straight as a distinct sexual identity subtype in young women.