Mostly heterosexual men describe themselves as slightly bisexual, with predominant sexual attraction to women but occasional attraction to men. After "completely heterosexual," "mostly heterosexual" is the most common male sexual orientation, by self-report. However, self-reported bisexual feelings among men can diverge from patterns of genital arousal, an objective measure of sexual interest with high validity. We compared 49 mostly heterosexual and 50 completely heterosexual men's patterns of genital and subjective sexual arousal to male and female erotic stimuli. In addition, we compared these groups on relevant self-report measures pertaining to sexual feelings, identity, and behavior. Results supported increased bisexual arousal with respect to self-report and genital arousal pattern among the mostly heterosexual men, compared with the completely heterosexual men. Furthermore, mostly heterosexual men reported more childhood gender nonconformity, greater male sex partners, and less self-reported disgust or aversion to sex acts with men. "Mostly heterosexual" appears to be a gradation of male sexual orientation associated with unique genital arousal patterns, among other correlates.
Keywords: Bisexuality; Mostly heterosexual; Sexual arousal; Sexual orientation.