Abstract:We use data from the 2002-2013 National Surveys of Family Growth to examine change across U.S. cohorts born between 1966 and 1995 in whether individuals have had sex with same-sex partners only, or with both men and women, and in whether they have a bisexual or gay identity. Adjusted for age, race/ethnicity, immigrant status, and mother's education, we find increases across cohorts in the proportion of women who report a bisexual identity, who report ever having had sex with both sexes, or who report having had sex with women only. By contrast, we find no cohort trend for men; roughly 5 percent of men in every cohort have ever had sex with a man, and the proportion claiming a gay or bisexual attraction changed little. We speculate that this gender difference is rooted in a broader pattern of asymmetry in gender change in which departures from traditional gender norms are more acceptable for women than men.Keywords: sexualities; gender; bisexuality; homosexuality; cohorts I T is often recognized that norms about gender and sexuality are linked, such that one violates gender norms by identifying as gay or bisexual, or by having sex with a same-sex partner (Pascoe 2007;England 2016). What is less often recognized is a link between trends in the gender and sexuality systems. Gender change has been asymmetric, with women taking on traditionally male activities more than vice versa (England 2010). Consistent with this more general pattern, we will show that the proportion of women who have had sex with a same-sex partner or who identify as bisexual has increased, with no parallel change for men.Several recent papers, focused mostly on period change in the 1990s and early 2000s, note an upward trend in sex with same-sex partners (Turner et al. 2005;Butler 2005;Twenge et al. 2016). Our study takes a cohort rather than period perspective, examining change across birth cohorts born between 1966 and 1995. We use data from the National Surveys of Family Growth (NSFG) collected between 2002 and 2013. Separately for men and women, we examine change across cohorts in sex with same-sex partners and in gay or bisexual identities using models that adjust for respondents' age, race, ethnicity, immigrant status, and socioeconomic background (measured with mother's education). We also examine whether trends have been significantly different along these dimensions. To foreshadow, we find substantial evidence of increases in women's sexual behavior with same-sex partners and in women's bisexual identity, but little change for men. We also find that trends differ little by race, ethnicity, immigration status, or socioeconomic background.