This study examined the association between sexual identity and substance use among undergraduates through surveying a random sample of 7000 students attending the University of Michigan. (Data from the same sample is also presented in Boyd et al. 2003). 3607 students (52% of the sample) responded to the survey. 58% of respondents were female, and 68% were White, so that respondents differ in gender and race/ethnicity from the university population. 3.3% (119, 65 women, 54 men) indicated they were lesbian/gay or bisexual. This paper did not report on lifetime or monthly Ecstasy use; figures can be found in Boyd et al 2003. (10% (or 361) students reported any lifetime use of Ecstasy, 7% (252) reported Ecstasy use in the past year, and 3% (108) reported having used Ecstasy in the past month.) Logistical regressions compared substance use in gay or bisexual and heterosexual students of the same gender (compared within gender), using ethnicity, class year, living arrangement (home/apartment, dormitory, fraternity/sorority, other), and GPA. Lesbian and bisexual women were more likely to have used cannabis in the last month and year, to have initiated cannabis use prior to college, and to have used Ecstasy within the last year than heterosexual women. They were also more likely to be polydrug users than heterosexual women. Gay and bisexual men were more likely to report annual cannabis and Ecstasy use than heterosexual men, yet they were less likely to report episodic drinking, did not differ in monthly or pre-university cannabis use, and were no more likely to be polydrug users than heterosexual men. (Comparisons are also made of adverse effects of drinking reported by gay, lesbian or bisexual respondents and heterosexual respondents). The authors do not seek to explain their findings of greater substance use in gay or bisexual students, but it seems likely to be multiply determined (life stress from sexual orientation, stronger risk taking in those coming out before or during university). No comparisons were made across genders. Study findings suggest that substance use, including Ecstasy use, may be higher in self-identified gay or bisexual young adults.