Objectives: Using data collected as part of the Multisite Women's Health Study, we examined the differences between lesbians and heterosexual women on objective breast cancer risk calculations using the Gail Model. Health risk behaviors and screening behaviors for breast cancer were also examined. It was hypothesized that lesbians would have higher objective cancer risk estimates and report more behavioral and screening risk factors for breast cancer than heterosexual women. Methods: Secondary data analyses were conducted using data from a study of women's health conducted from 1994 to 1996. Using a cross sectional design, a convenience sample of lesbian (n = 550) and heterosexual (n = 279) women was recruited from Chicago, New York City and Minneapolis-St. Paul. Data were collected using a self-administered questionnaire. Results: Estimates of 5-year and lifetime breast cancer risk were higher for lesbians compared to heterosexual women. Groups did not differ in self-perceptions of being overweight, but more lesbians reported heavier drinking and more reported abstinence from alcohol. Group differences in adherence to breast cancer screening were not significant. Conclusions: Findings suggest a small but statistically significant difference in the calculated breast cancer risk estimates of lesbian and heterosexual women, which seem to be largely accounted for by differences in reproductive risk factors.