BACKGROUND: Despite knowledge that some people engage in same-sex sexuality without espousing a sexual minority identity, this has rarely been studied in women. METHODS: Heterosexual women aged 20 to 44 who indicated one or more female sex partners in the past year were compared to those with less recent female sex partners, and to bisexual, homosexual, and exclusively heterosexual women using 2002 US National Survey of Family Growth data. RESULTS: Compared to exclusively heterosexual women, heterosexual women with a past-year female sex partner were significantly more likely to smoke tobacco (46% vs. 19%), binge drink (34% vs. 11%), use marijuana (58% vs. 11%), and use cocaine (19% vs. 2%). Substance use was high in this group overall, but they did not differ significantly from bisexuals on tobacco use or from homosexual or bisexual women on regular alcohol consumption. Most heterosexual women with a past-year female sex partner had only one in their lifetime. They had 10 median lifetime male partners versus 1 to 7 for other groups. Whereas similar to heterosexual women with less recent female sex partners and to bisexual women on some sexual risk measures, these women were more likely than any other group to have had a non-monogamous male partner (40%) or to have engaged in sex while high (69%). Differences in sexual risk and substance use were not explained by demographic differences. CONCLUSIONS: Results suggest same-sex behavior in heterosexual-identified women is a marker for a substance use and sexual risk profile distinct from that of bisexual, lesbian, or exclusively heterosexual women.