In the literature about bisexuality few studies consider bisexual people’s beliefs about bisexuality and none examine essentialist beliefs about bisexuality. In the present study 244 participants (bisexual n = 58, lesbian/gay n = 54 and heterosexual n = 132) from the UK were asked via online questionnaire about their attitudes towards bisexuality, homosexuality and heterosexuality, and how stable they perceived bisexuality, homosexuality and heterosexuality to be. They were also asked about their essentialist beliefs towards bisexuality. Bisexual respondents viewed bisexuality as significantly more stable than lesbian, gay and heterosexual respondents. Analysis also showed that less belief in the discreetness of bisexuality predicted more positive attitudes towards bisexuality, as did positive beliefs towards homosexuality and heterosexuality. Belief in the immutability of bisexuality did not, however, predict attitudes towards bisexuality. Therefore, discreteness appears to be an especially problematic essentialist belief about all sexual minorities, as it is consistently associated with negative attitudes. However, beliefs about the immutability of sexuality are not consistently associated with negative attitudes for all sexual minorities.