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Recent research has revealed a reliable sex difference in geni-tal response patterns. Men’s genital responses are category-specific, in that men tend to exhibit high responses to only certain stimulus categories. For example, self-identified het-erosexual men exhibit large genital responses to sexual stimuli depicting adult women and no response to adult men (Lykins et al., 2010). In contrast, women’s genital responses are typi-cally category-nonspecific: Women tend to exhibit similar responses to a variety of sexual stimuli. For example, self-identified heterosexual women show similar responses to stimuli that depict heterosexual, gay, or lesbian sex (Chivers, Rieger, Latty, & Bailey, 2004). In this study, we tested a func-tional hypothesis for women’s category-nonspecific genital responses: that women’s genital responses function to prepare the body for sexual intercourse, whether it is wanted or not