Debates persist over whether bisexuality is a temporary stage of denial or transition, a stable "3rd type" of sexual orientation, or a heightened capacity for sexual fluidity. The present study uses 5 waves of longitudinal data collected from 79 lesbian, bisexual, and "unlabeled" women to evaluate these models. Both the "3rd orientation" and "fluidity" models had support, but the "transitional stage" model did not. Over 10 years, 2/3 of women changed the identity labels they had claimed at the beginning of the study, and 1/3 changed labels 2 or more times. Yet, contrary to the "transitional stage" model, more women adopted bisexual/unlabeled identities than relinquished these identities; few bisexual/unlabeled women ended up identifying as lesbian or heterosexual. Overall, the most commonly adopted identity was "unlabeled." Bisexual/unlabeled women had stable overall distributions of same-sex/other-sex attractions but greater absolute fluctuations in attractions from assessment to assessment than lesbians. All women reported declines in their ratio of same-sex to other-sex behavior over time. These findings demonstrate that the distinction between lesbianism and bisexuality is a matter of degree rather than kind.